Hydrotalcite compound, process for producing the same, and agricultural film containing the same

ABSTRACT

A hydrotalcite compound which has the excellent ability to absorb infrared rays and has excellent light transmission when contained in an agricultural film; a process for producing the compound; and an infrared absorber and an agricultural film both containing the compound. The hydrotalcite compound is characterized by retaining as the interlayer anions at least one kind of anions selected among ions of silicon-, phosphorus-, and boron-containing polymeric oxyacids and another kind of anions.

TECHNICAL FIELD

This invention relates to hydrotalcite compound which has excellentinfrared absorption ability and a characteristic property of exhibitingexcellent light-transmission when it is contained in agricultural film;a process for producing the same; infrared absorbing agent containingsaid hydrotalcite compound as the active ingredient; and agriculturalfilm which contains said infrared absorbing agent.

BACKGROUND ART

Agricultural films have been widely used for greenhouse cultivation ortunnel cultivation of agricultural products. Those agricultural filmsare required to concurrently exhibit good light transmission and heatinsulating property. That is, temperatures within a greenhouse or tunnelwhich are raised by the daytime sunbeams of 0.29-4.3 μm in wavelengthrapidly drop in night, in particular, clear weather night, due toradiational cooling. Such rapid temperature drop inside a greenhouse ortunnel incurs adverse effect on growth of crops. While various causesare considered to induce the rapid temperature drop, there is an opinionthat heat radiation from surface of the earth or cultivated plants tothe outside atmosphere (radiation as long wavelength infrared rays) innights is the reason for the temperature drop. According to that view,the heat radiation is calculated, using Planck's formula, i.e., thefollowing formula (3), as black body radiation energy:

Eλ·dλ(erg. sec⁻¹.cm⁻²) Eλ·dλ=2πhC{circumflex over ( )}2/[λ{circumflexover ( )}5{e{circumflex over ( )}(hC/λkT)−1}]·dλ  (3)

in which

λ: wavelength

h: Planck's constant

C: velocity of light in vacuum

k: Boltzmann's constant

T: absolute temperature.

From the calculation, it is explained that the rays of wavelengthswithin the infrared region, in particular, infrared rays (black bodyradiation energy) of 400-2000 cm⁻¹, the maximum being at 1000 cm⁻¹, aresaid to be emitted within the temperature range of from 30 to −10° C. toinduce the temperature drop.

For preventing such rapid temperature drop inside a greenhouse ortunnel, heat insulating film having infrared-absorbing ability is used.Such heat insulating film is provided by either using, as thermoplasticresin which is the base material, the one having infrared absorbingability itself or the one to which a substance having ability to absorbinfrared rays (in particular, rays of wave-lengths ranging 400-2000cm⁻¹), i.e., an infrared absorbing agent, is blended so as to impart tothe film infrared absorbability. As infrared absorbers, for example,silica; silicate; hydroxide, oxide, aluminate, borate or sulfate oflithium, calcium, magnesium or aluminium; or hydrotalcite compounds areused.

Of those, hydrotalcite compounds excel in infrared absorbing ability andlight transmission when blended in resin, over those of silica;silicate; or hydroxide, oxide, aluminate, borate or sulfate of lithium,calcium, magnesium or aluminium and, therefore, are particularly usefulas infrared absorbing agents, and many patent applications have beenfiled on inventions relating thereto. (Hydrotalcites are complexhydroxide having lamellar structures formed of complex hydroxide layers(base layers) of Mg and Al, separated by interlayer wherein holdinganions (e.g., carbonate ions) and water. Those which are represented bythe formulae (1) or (4) in the present specification are complexhydroxides having base layers formed of Mg and Al; or Mg, other divalentmetal(s) and Al, holding anions and water in the interlayer. Whereas,those represented by the formulae (2) or (5) also are complex hydroxidesdiffering in composition of the base layers, having base layers formedof Li and Al; or Li, other divalent metal(s) and Al, holding anions andwater in the interlayer. All of those have structures similar oranalogous to those of hydrotalcite, and hence they are collectivelyreferred to as “hydrotalcite compounds” in the present specification.Those which are expressed by the formula (1) or (4) are referred to asMg—Al hydrotalcite compounds, and those of formula (2) or (5), as Li—Alhydrotalcite compounds).

Among patent applications filed in the past on inventions relating toMg—Al hydrotalcite compounds, there are, for examples, Sho 62(1987)-31744B-JP (corres. to U.S. Pat. No. 4,686,791 and EP 142,773),Sho 62-53543B-JP, Sho 62-41247B-JP, Sho 63 (1988)-175072B-JP, Sho63-115743B-JP, Sho 63-149147B-JP, Sho 63-149148B-JP, Sho 64(1989)-6041B-JP, Hei 4 (1992)-11107B-JP, Hei 6 (1994)-6363B-JP, Hei6-6364B-JP and Hei 9 (1997)-176390A-JP. Examples of those relating toLi—Al hydrotalcite compounds include: Hei 7 (1995)-300313A-JP (corres.to EP 672,619), Hei 9 (1997)-142835A-JP (corres. to EP 790,214), Hei9-279124A-JP, Hei 9-800828A (second)-JP (corres. to U.S. Pat. No.5,767,179 and EP 778,241) [This is the domestic republication of PCTinternational publication for the patent application. Similar case shallbe hereafter marked as “A (second)”], Hei 9 (1997)-235420A-JP (corres.to EP 781,800), Hei 10 (1998)-52895A-JP, Hei 10-235776A-JP and Hei10-226739A-JP.

While the hydrotalcite compounds are expressed by various structuralformula in these patent applications, they can be generally representedby the following formula (4) or (5).

(General formula of Mg—Al hydrotalcite compounds): $\begin{matrix}{{\underset{({{base}\quad {layer}})}{\left\lbrack {\left\{ {{Mg}_{y1}M_{y2}^{2 +}} \right\}_{1 - X}{{Al}_{X}({OH})}_{2}} \right\rbrack}}^{X +}{\underset{({interlayer})}{\left\lbrack {{A_{X/n}^{n -} \cdot b}\quad H_{2}O} \right\rbrack}}^{X -}} & (4)\end{matrix}$

in the above formula,

M²⁺ stands for at least one kind of divalent metal ion of Zn, Ca and Ni,

A^(n−) stand for a n-valent anion of, e.g., inorganic or organic acidsuch Cl⁻, Br⁻, I⁻, NO₃ ⁻, CIO₄ ⁻, H₂PO₄ ⁻, HBO₃ ²⁻, SO₄ ²⁻, CO₃ ²⁻, SiO₃²⁻, HPO₄ ²⁻, PO₄ ³⁻, Fe(CN)₆ ³⁻ and Fe(CN)₄ ⁴⁻,

and x, y₁, y₂ and b are positive numbers each satisfying the followingconditions, respectively,

0<x≦0.5, y₁+y₂=1, y₁≦1, y₂<1, 0≦b<2.

(General formula of Li—Al hydrotalcite compounds) $\begin{matrix}{\underset{({{base}\quad {layer}})}{\left\lbrack {\left( {{Li}_{1 - X}G_{X}^{2 +}} \right){{Al}_{2}({OH})}_{6}} \right\rbrack^{{({1 + X})} +}}{\underset{({interlayer})}{\left\lbrack {{\left( A^{n -} \right)_{{({1 + X})}/n} \cdot b}\quad H_{2}O} \right\rbrack}}^{{({1 + X})} -}} & (5)\end{matrix}$

in which

G²⁺ stands for at least one kind of divalent metal ion of Mg, Zn, Ca andNi,

A^(n−) stands for a n-valent anion,

and x and b are positive numbers each satisfying the followingconditions, respectively,

0≦x<1, 0≦b<5.

Of these, in most cases hydrotalcite compounds having carbonate ions inthe interlayer (which are hereafter referred to as carbonate ion-typehydrotalcite compounds) are used.

Taking examples of carbonate ion-type Mg—Al hydrotalcite compounds,however, while they exhibit favorable absorption of infrared rays around400-800 cm⁻¹ and 1400 cm⁻¹, the absorbing ability of the infrared raysof 900 to around 1300 cm⁻¹ is poor. When they are contained inagricultural film whose base material is polyethylene exhibitinginfrared absorption at around 700 and 1300-1500 cm⁻¹ only, theagricultural film exhibits combined infrared absorption of that of thepolyethylene and that of the infrared absorbing agent and hence showspoor infrared absorption in the vicinity of 900-1300 cm⁻¹, i.e., poorheat-insulation property. Also carbonate ion-type Li—Al hydrotalcitecompounds show infrared absorbing ability at around 1000 cm⁻¹ whichhowever is not strong, and their over-all infrared absorbing ability isabout the same as that of carbonate ion type Mg—Al hydrotalcitecompounds. Agricultural films containing those compounds, furthermore,are considered to exhibit better light transmission compared to that ofthe films containing other infrared absorbing agents, but still thelight transmission is not fully satisfactory.

As a means to enhance the infrared absorbing ability of Mg—Alhydrotalcite compounds, Sho 62 (1987)-31744B-JP (corres. to U.S. Pat.No. 4,686,791 and EP 142,773) proposed to impart thereto the ability toabsorb infrared rays around 900-1300 cm⁻¹ by having them contain H₂PO₄⁻, HPO₄ ²⁻, PO₄ ³⁻, HBO₃ ²⁻ or SiO₃ ²⁻ and the like, i.e., thosenormally referred to as silicon-, phosphorus- and boron-containingmonomeric oxygen acid ions, in the interlayer. A similar proposal wasmade also as to Li—Al hydrotalcite compounds. However, when hydrotalcitecompounds containing these anions are used as infrared absorbing agentsin agricultural film, some improvement in heat insulation of the film isachieved but it is still not fully satisfactory. Furthermore, theability to impart light transmission to film is either equivalent orinferior to that of conventional carbonate ion-type hydrotalcitecompounds.

Recently, proposals for further improving infrared absorption ofhydrotalcite compounds are made in Hei 8 (1996)-217912A-JP (corres. toEP 708,056) or Hei 9 (1997)-800828A (second)-JP (corres. to U.S. Pat.No. 5,767,179 and EP 778,241), according to which condensed silicateions and/or condensed phosphate ions (which are hereafter referred to assilicon- and/or phosphorus-containing polymerized oxygen acid ion) arecaused to be present as the interlayer anions of hydrotalcite compounds.The object of these proposals is to improve the infrared absorption byhaving the compounds contain more silicon- or phosphorus-containingoxygen acid ions in their interlayer, by the use of silicon- orphosphorus-containing polymerized oxygen acid ions. It is furthermorealleged that those methods can approximate refractive indices of theresulting hydrotalcite compounds to those of thermoplastic resinsconstituting agricultural films and hence can improve light transmissionof the films which contain said hydrotalcite compounds. Morespecifically, while spacing of carbonate ion-type hydrotalcite compoundsis about 7.6 Å at (003) plane or (002) plane, and their refractive indexranges 1.51-1.53, those hydrotalcite compounds shown in Hei 8-217912A-JP(corres. to EP 708,056) or Hei 9-800828A (second)-JP (corres. to U.S.Pat. No. 5,767,179 and EP 778,241), e.g., those havingsilicon-containing polymerized oxygen acid ions, have increased spacingof 11.9 Å at the maximum at (003) or (002) planes, and whereby theirrefractive index decreases to 1.49-1.52. Refractive index ofthermoplastic resin useful for agricultural film, e.g., anethylene-vinyl acetate copolymer, is said to be 1.49-1.50. Henceagricultural films containing the hydrotalcite compounds as exemplifiedin above two published patent applications are said to exhibit improvedlight transmission.

However, our reproduction testing of such agricultural films hasrevealed: although the agricultural films exhibited improved infraredabsorption, their light transmission again was at equivalent or inferiorlevel as compared to that of films containing conventional hydrotalcitecompounds. While the reason for the absence of improvement in lighttransmission of the film is not yet fully clear, one of suspected causesis the processing temperature used in the occasion of kneading such asilicon- or phosphorus-containing polymerized oxygen acid ion-carryinghydrotalcite compound into the resin serving as the material foragricultural film, as disclosed in said two published applications.

Thus, none of known infrared absorbing agent in the past could fullysatisfy both of the property requirements to have excellent infraredabsorption and, when contained in agricultural film, to impart goodlight transmission to the film.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a substance which hasexcellent infrared absorbing ability and also is capable of impartingexcellent light transmission to an agricultural film containing saidsubstance; a process for production thereof, an infrared absorbing agentcontaining the substance as the active ingredient; and an agriculturalfilm containing said infrared absorbing agent, which concurrentlyexhibits excellent heat insulation property and excellent lighttransmission.

We have engaged in research work aiming at accomplishing the aboveobject, to discover that a hydrotalcite compound which is expressed bythe following formula (1) or (2) and which holds in its interlayer atleast a kind of anions selected from silicon-, phosphorus andboron-containing oxygen acid ions, at least a part of said anions beingat least one of silicon-, phosphorus- and boron-containing polymerizedoxygen acid ions; and other kind or kinds or anions, exhibits excellentinfrared absorbing ability and is capable of imparting excellent lighttransmission to an agricultural film containing the same. The inventionis thus completed. When said hydrotalcite compound is contained inagricultural film as an infrared absorbing agent, a film excelling inheat insulation as well as in light transmission is obtained:

(Mg—Al hydrotalcite compound)

in which

M²⁺ stands for at least a kind of divalent metal ion of Zn, Ca and Ni,

A stands for at least a kind of anion selected from silicon-,phosphorus- and boron-containing oxygen acid ions, at least a part ofwhich being at least a kind of anion selected from silicon-, phosphorus-and boron-containing polymerized oxygen acid ions,

B stands for at least a kind of anion other than the A, and

x, y₁, y₂, z₁, z₂ and b each satisfies the following condition orconditions:

x: 0<x≦0.5,

y₁ and y₂: y₁+y₂=1, 0<y₁≦1, 0≦y₂<1,

z₁ and z₂: 0<z₁, 0<z_(2,)

b: 0≦b<2.

(Li—Al hydrotalcite compound)

in which

G²⁺ stands for at least a kind of divalent metal ion of Mg, Zn, Ca andNi,

A stands for at least a kind of anion selected from silicon-,phosphorus- and boron-containing oxygen acid ions, at least a part ofwhich being at least a kind of anion selected from silicon-, phosphorus-and boron-containing polymerized oxygen acid ions,

B stands for at least an anion other than the A, and y₁, y₂, x, z₁, z₂and b each satisfies the following condition or conditions:

y₁ and y₂: 0<y₁≦1, 0<y₂<1,

0.5≦(y₁+y₂)≦1,

x: x=y₁+2y₂

z₁ and z₂: 0<z₁, 0<z₂,

b: 0≦b<5.

That is, the hydrotalcite compound of the invention contains between itsbase layers: as A, at least a kind of anion selected from silicon-,phosphorus- and boron-containing oxygen acid ions, at least a part ofwhich being at least a kind of anion selected from silicon-, phosphorus-and boron-containing polymerized oxygen acid ions (which anions beinghereafter referred to as “A anions”) and as B, anion or anions otherthan A (“B anions”), which characteristically exhibits concurrentlyexcellent infrared absorption and an ability to impart excellent lighttransmission to agricultural film containing same. Such combination ofproperties has never been obtained when any known hydrotalcite compoundscontaining various ions, or those containing silicon- orphosphorus-containing polymerized oxygen acid ions as disclosed in Hei8-217912A-JP (corres. to EP 708,056) or Hei 9-800828A (second)-JP(corres. to U.S. Pat. No. 5,767,179 and EP 778,241), or theircombinations are used as infrared absorbing agent.

The reason for these advantageous properties is not yet 10 fully clear.Whereas, those hydrotalcite compounds carrying silicon- orphosphorus-containing polymerized oxygen acid ions as disclosed in Hei8-217912A-JP (corres. to EP 708,056) or Hei 9-800828A (second)-JP(corres. to U.S. Pat. No. 5,767,179 and EP 778,241) and which contain alarge amount of interlayer water have notably widened spacing asaforesaid, and their refractive index is approximate to that ofthermoplastic resins which are used for agricultural films. Due to sowidened spacing, according to DTA (differential thermal analysis) theinterlayer water is released at temperatures not higher than 150° C. Onthe other hand, in the occasion of blending an infrared absorbing agentinto thermoplastic resin to be used for agricultural film, normally theyare kneaded at processing temperatures ranging 140-200° C. Hence, whensaid hydrotalcite compound is blended as an infrared absorbing agent ina thermoplastic resin to be used to make agricultural film, theinterlayer water in the infrared absorbing agent is released under theprocessing temperature of 140-200° C. to once again narrow the widenedspacing. In consequence, its refractive index also largely changes, andeventually when the composition is processed to a film, the filmpresumably comes to exhibit poor light transmission. This assumption issupported also by the phenomenon that the percent transmission of thefilm further drops when interlayer water of the infrared absorbing agentis removed in advance of its kneading into the thermoplastic resin andthe kneaded composition is processed into film. Furthermore, theinfrared absorbing agent contains large amounts of silicon- orphosphorus-containing polymerized oxygen acid ions, which allows aprediction that locally silicate or phosphate compounds are formedinside the crystals (interlayer) during synthesis of the compound orduring the release of interlayer water under the heat treatment, and soformed silicate or phosphate compounds may adversely affect lighttransmission of the product film.

Separately from above assumptions, it is known that interlayer water ofhydrotalcite compounds containing anions other than A anions, forexample, sulphate ion, carbonate ion, chloride ion or nitrate ion, isreleased at around 200-240° C. The hydrotalcite compound of theinvention contains both A anions and B anions and, for example, when itcontains as B anions sulphate ion, carbonate ion, chloride ion, nitrateion and the like, the property of hydrotalcite compound having such ionsat its interlayer is added to the hydrotalcite compound of theinvention. Consequently, even under the processing temperature of140-200° C. it retains a part of interlayer water to alleviate thenarrowing ratio of the spacing and in consequence reduces the change inrefractive index. Hence when the compound of the present invention isblended in agricultural film as an infrared absorbing agent, itpresumably exhibits little adverse effect on light transmission of thefilm. Also because the hydrotalcite compound of the invention uniformlycontains the plural kinds of anions in the interlayer, presumablyformation of silicate compound or phosphate compound scarcely takesplace.

The interlayer B anions in the hydrotalcite compound of the invention isat least a kind of anion other than A anions, i.e., other than silicon-,phosphorus- and boron-containing oxygen acid ions, preferably thoseselected from sulphate ion, carbonate ion, chloride ion and nitrate ion,inter alia, sulphate ion and carbonate ion.

When the compound of the invention is to be contained, for example, inresin, the compound preferably has an average secondary particlediameter of not more than 5 μm and a BET specific surface area of notmore than 30 m²/g, for favorable dispersibility. In order to furtherimprove the dispersibility, it may be surface-treated with at least onemember of the group consisting of higher fatty acids; anionicsurfactants; phosphoric acid esters; nonionic surfactants, silane-,titanate- and aluminum-containing coupling agents; and fatty acid estersof polyhydric alcohols. Also for avoiding occurrence of foaming orfish-eye, the hydrotalcite compound of the invention which has beenoptionally surface-treated may be partially or entirely removed of theinterlayer water by a heat-treatment.

The hydrotalcite compound of the present invention has excellentinfrared absorbing ability and the property of imparting excellent lighttransmission to agricultural film which contains the same, and thereforeis suitable as infrared absorbing agent for agricultural films. Inparticular, referring to the formulae (1) and (2), 20 those compoundswhose electric charges fall within the range of 0.1≦(total electriccharge number of (B)z₁)/x≦0.8 are preferred as infrared absorbing agent.Thus, an agricultural film which contains 1-30% by weight of ahydrotalcite compound of the invention to the thermoplastic resinconstituting the film concurrently possesses excellent infraredabsorbing ability and excellent light transmission.

The hydrotalcite compound of the present invention can be prepared by aprocess comprising preparing in advance a hydrotalcite compound whoseinterlayer anions are of at least one kind of anions other than Aanions, for example, sulphate ions, carbonate ions, chloride ions,nitrate ions or an organic acid ions, and then exchanging some of themwith A anions. In particular, it is preferred to first prepare ahydrotalcite compound whose interlayer anions are of at least one kindof selected from sulphate ion, carbonate ion, chloride ion and nitrateion, and then exchanging a part of them with A anions. The optimumresult can be obtained, furthermore, by preparing a hydrotalcitecompound containing mainly sulphate ions at the time of the synthesizingreaction and then exchanging some of the sulphate ions with A anions,because it can be prepared with ease and at low cost, and furthermore itassists the infrared absorbing ability which shall be discussed later.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an IR absorption chart of a 100 μm-thick film of metallocenepolyethylene (PE) containing 10% by weight of the hydrotalcite compound(powder) of the present invention as obtained in Example 2.

FIG. 2 is an IR absorption chart of a 100 μm-thick film of metallocenePE containing 10% by weight of the hydrotalcite compound (powder) of thepresent invention as obtained in Example 3.

FIG. 3 is an IR absorption chart of a 100 μm-thick film of metallocenePE containing 10% by weight of the hydrotalcite compound (powder) of thepresent invention as obtained in Example 9.

FIG. 4 is an IR absorption chart of a 100 μm-thick film of metallocenePE containing 10% by weight of the hydrotalcite compound (powder) asobtained in Comparative Example 1.

FIG. 5 is an IR absorption chart of a 100 μm-thick film of metallocenePE alone.

BEST MODE FOR CARRYING OUT THE INVENTION

The hydrotalcite compound of the invention can be prepared as follows.For preparation of Mg—Al hydrotalcite compound, those methods asdisclosed in Sho 47 (1972)-32198B-JP (corres. to U.S. Pat. No.3,796,792), Sho 50 (1975)-30039B-JP, Sho 51 (1976)-29129B-JP, or Hei 4(1992)-73457B-JP (corres. to U.S. Pat. No. 4,675,356 and EP 189,899) areknown, according to which, by suitably selecting and reacting aqueoussolutions of, for example, chloride, sulphate, nitrate, carbonate orhydroxide of Mg, M²⁺ or Al and alkaline aqueous solutions of sodiumhydroxide, sodium carbonate, sodium aluminate and the like, for example,slurry of Mg—Al hydrotalcite compound having sulphate ion, carbonateion, chloride ion or nitrate ion at its interlayer can be synthesized.For example, where synthesis of a Mg—Al hydrotalcite having sulphateions at its interlayer is intended, aqueous solutions of chlorides of Mgand M²⁺, aluminium sulphate and sodium hydroxide are used in thereaction to provide the object product. The molar ratios among Mg, M²⁺and Al can be optionally selected within the ranges specified by formula(1). Whereas, x preferably is within the range of 0.2≦x≦0.5, inparticular, 0.2≦x≦0.4, inter alia, 0.25≦x≦0.35. Because those elementswhich are named as examples of M²⁺ have atomic weights greater than thatof Mg, when the molar ratio of M²⁺ rises, the molecular weight ofresulting Mg—Al hydrotalcite compound increases correspondingly, toeventually reduce infrared absorption of the infrared absorbing agent.Hence, lower molar ratio of M²⁺ is preferred. More specifically y₂≦0.5,in particular, y₂≦0.3, is preferred. Subsequently, so synthesized slurryof Mg—Al hydrotalcite compound is given a hydrothermal treatment in anaqueous medium, under such conditions as: for example, at temperaturesof about 120° C.-about 250° C. for about 1-about 40 hours, to form aslurry of Mg—Al hydrotalcite compound whose average secondary particlediameter and BET specific surface area are adjusted.

As methods for preparing Li—Al hydrotalcite compound, those disclosed inHei 9 (1997)-142835A-JP (corres. to EP 790,214) or Hei 9-279124A-JP areknown, according to which a slurry of Li—Al hydrotalcite compoundhaving, for example, sulphate ion, carbonate ion, chloride ion ornitrate ion as interlayer anions, is synthesized through reaction ofsuitably selected aqueous solutions of, for example, chlorides,sulfates, nitrates, carbonates or hydroxides of Li, G²⁺ and Al, oralkaline solutions of sodium hydroxide, sodium carbonate, sodiumaluminate and the like. For example, when synthesis of a slurry of Li—Alhydrotalcite compound containing sulfate ions in its interlayer isintended, aqueous solutions of chlorides of Li and G²⁺ and those ofaluminium sulfate and sodium hydroxide are reacted to obtain theintended slurry. The molar ratio of Li G²⁺, and Al can be optionallyselected within the ranges specified by the formula (2). Whereas, as toy₁+y₂, 0.7≦(y₁+y₂)≦1, in particular, 0.9≦(y₁+y₂)≦1, inter alia.0.95≦(y₁+y₂)≦1 is preferred. The molr ratio between Li and G²⁺ ispreferably low, because a high molar ratio of G²⁺ makes it difficult tomaintain the structure of the Li—Al hydrotalcite compound. Hence,y₂≦0.5, in particular, y₂≦0.2, inter alia, y₂≦0.1, is preferred. Theresulting slurry of Li—Al hydrotalcite compound is then given ahydrothermal treatment in an aqueous medium, under such conditions as:at temperatures of about 80° C.-about 250° C. for about 1-about 40hours, to form a slurry of Li—Al hydrotalcite compound whose averagesecondary particle diameter and BET specific surface area are adjusted.

Then, the slurry of Mg—Al or Li—Al hydrotalcite compound (excepting thatof carbonate ion type) is mixed with a solution containing at least oneof silicon-, phosphorus- and boron-containing oxygen acid ions, wherebythe anions incorporated at the time of synthesis undergo ion-exchangewith the silicon-, phosphorus- and boron-containing oxygen acid ions,allowing formation of a hydrotalcite compound having, for example, Aanions and at least one of sulphate ion, carbonate ion, chloride ion andnitrate ion as the interlayer anions and having suitably adjustedaverage secondary particle diameter and BET specific surface area.

Furthermore, for effecting the ion-exchange to A anions in the slurry ofa carbonate ion-type Mg—Al or Li—Al hydrotalcite compound which issynthesized by the above-described method, a part or whole of theinterlayer carbonate ions are exchanged with sulphate ion, carbonateion, chloride ion, nitrate ion or organic acid ion in advance usingsolutions of low molecular weight organic acids such as sulfuric,hydrochloric, nitric or acetic acids, followed by further ion-exchangeusing an alkaline substance such as sodium silicate, sodium phosphate orsodium borate. Or, partial ion-exchange with the carbonate ions may bedirectly carried out using an acid such as phosphoric acid.

In the above-described production methods, a surface-treating agent asdescribed later may be added before the ion-exchange to A anions toeffect a surface treatment and then to carry out the ion-exchange to Aanions.

The hydrotalcite compound of the invention is not necessarily limited bythe above-described production methods, but may be produced by stillother methods. Actually, however, such other methods often invite risein the material or production costs. Also among the above-describedmethods, the one which uses an acid is liable to injure crystallinestructure of the hydrotalcite compound or to impair dispersibility ofthe compound. The use of acid may also give rise to a problem of carbondioxide gas generation during the production. Hence, it is preferred toprepare hydrotalcite compounds other than carbonate ion-type, at thestage of the synthesizing reaction. In particular, preparation ofhydrotalcite compound containing mainly sulphate ions as the interlayeranions is most convenient, because of ease and low costs andcomplementary effect for infrared absorption.

The ion-exchange to A anions can be effected by throwing solutioncontaining at least one of silicon-, phosphorus- and boron-containingoxygen acid ions into said hydrotalcite compound slurry under stirringand continuing the stirring at normal temperature for a minute-24 hours,preferably at 60° C. or above (heating of the slurry may start beforethe addition of said oxygen acid ions) for 1-24 hours, in particular, at70° C. or above for 1-24 hours, inter alia, at 80° C. or above for 1-24hours. Whereas, when the temperature is 100° C. or above, use of apressure vessel becomes necessary, and the stirring for longer than 24hours is undesirable from the standpoint of productivity.

The A anions to be contained in the hydrotalcite compound of the presentinvention are silicon-, phosphorus- and boron-containing oxygen acidions. For example, those containing silicon include monomeric oxygenacid ions or polymerized oxygen acid ions of the formulae(Si_(n)O_(2n+1))²⁺ or (HSi_(n)O_(2n+1))⁻ (n is an integer not less than1), such as SiO₃ ²⁻, Si₂O₅ ²⁻, Si₃O₇ ²⁻, Si₄O₉ ²⁻, (HSiO₃)⁻, (HSi₂O₅)⁻and the like may be named; as the phosphorus-containing oxygen acidions, PO₄ ³⁻, (HPO₄)²⁻, (H₂PO₄)⁻, (P₂O₇)⁴⁻, (P₃O₁₀)⁵⁻, or thoseexpressed by the formulae (P_(n)O_(3n))^(n−) or [(PO₃)_(n)]^(n−) (n isan integer not less than 3), such as (P₃O₉)³⁻, (P₄O₁₂)⁴⁻, (P₆O₁₈)⁶⁻ andthe like, or phosphorus-containing oxygen acid ions to which a number ofH radicals are added, such as (H₂P₂O₇)²⁻ may be named; and asboron-containing oxygen acid ions, BO₃ ³⁻, (HBO₃)²⁻, (H₂BO₃)−,[B₃O₃(OH)₄]⁻, [B₅O₆(OH)₄]⁻, [B₄O₅(OH)₄]²⁻ and the like may be named. Inthe hydrotalcite compound of the present invention, a part or all of theA anions is in the form of at least one of silicon-, phosphorus- orboron-containing polymerized oxygen acid ions, to achieve the objects ofinfrared absorption improvement and light transmission improvement inagricultural film containing the compound.

As specific starting materials of these silicon-, phosphorus- orboron-containing oxygen acid ions, sodium metasilicate, No. 1, 2 and 3water glasses or amorphous SiO₂ as dissolved in an aqueous alkali metalhydroxide solutions may be named as examples of silicon-containingmaterial, and as phosphorus-containing material, phosphoric acid oraqueous alkali metal solutions (inclusive of those containing hydrogenradical); and boric acid, sodium borate, sodium tetraborate and the likemay be named as examples of boron-containing material.

B is at least a kind of anion other than the A, examples of which beinginorganic acid ions such as chloride ion, bromide ion, iodide ion,nitrate ion, carbonate ion, sulphate ion, perchlorate ion, iron cyanideion and organic acid ions such as formate ion, acetate ion and oxalateion. Of those, at least one anion selected from sulphate ion, carbonateion, chloride ion and nitrate ion is preferred, in particular, sulphateion and carbonate ion being preferred. The optimum is sulphate ion whichshows infrared absorption in the vicinity of 1100 cm⁻¹, and even itslocal presence can improve infrared absorption of the hydrotalcitecompound.

When the hydrotalcite compound of the invention is used as an infraredabsorbing agent, while its content of silicon-, phosphorus- orboron-containing oxygen acid ions should be substantial, an excessivelyhigh content may invite reduction in infrared absorption attributable tothe base layers of primary hydrotalcite compound, or, when it is blendedin agricultural film, may cause drop in the latter's light transmission.Whereas, when the content is too low, the compound comes to exhibit poorinfrared absorption and hence cannot improve heat insulation property ofthe agricultural film in which it is blended. Thus, preferably A anionsoccupy 20-90%, in particular, 30-80%, of theoretical amount (totalelectric charge number: x⁻) of interlayer anions as calculated from thebase layers in formula (1) or (2) in claim 1.

While preferred content of silicon-, phosphorus-, and boron-containingoxygen acid ions is as addressed in the above paragraph, in practice itis known that silicon-, phosphorus- or boron-containing oxygen acid ionshave various forms, and it is difficult to determine the forms of thesilicon-, phosphorus- or boron-containing oxygen acid ions present ininterlayer of the hydrotalcite compound locally containing thoseinterlayer anions. Consequently, it is also difficult to limit theelectric charges of the oxygen acid ions. Still more difficult is todetermine the ratio of the electric charge of the oxygen acid ions tothe total electric charge number of the interlayer anions. We looked foran alternative means for determining it to find that it can beconveniently expressed by the ratio of electric charge numbers of theanions other than A, i.e., of the B anions which are present in theinterlayer. Expressed in this way, it is preferred for the totalelectric charge number of B anions to amount to 10-80% of the totalelectric charge number of interlayer anions, i.e., 0.1≦(total electriccharge number of (B)z₁)/x≦0.8, in particular, 20-70%, i.e., 0.2≦(totalelectric charge number of(B)z₁)/x≦0.7.

The hydrotalcite compound of the invention may be removed of a part orwhole of its interlayer water, by heating its powder at temperatures of150-250° C. for 1-20 hours.

The hydrotalcite compound holding A anions and B anions as theinterlayer anions according to the invention can be distinguished fromconventional hydrotalcite compounds by such means as powder X-raydiffraction (XRD), composition analysis or infrared absorption spectrumanalysis.

Upon examining formation of hydrotalcite compound or spacing of thelayers through the diffraction patterns obtained by XRD, presence ofsilicon-, phosphorus- and boron-containing polymerized oxygen acid ionsheld in the interlayer can be confirmed. For example, spacing ofcarbonate ion-, chloride ion-, or silicon-containing monomeric oxygenacid ion-type hydrotalcite compound as determined by XRD is 7.4-7.8 Å at(003) or (002) plane; and that of sulphate ion-, nitrate ion- orphosphorus-containing monomeric oxygen acid ion-type hydrotalcitecompound, 8.2-8.8 Å at (003) or (002) plane. When those ions in thesehydrotalcite compounds are exchanged with, e.g., silicon-, phosphorus-and boron-containing polymerized oxygen acid ions, the spacing at (003)or (002) plane in most cases increases to 9 Å or more. Whereby it ispossible to predict whether or not such polymerized oxygen acid ions arepresent in the interlayer. This statement may not apply, however, whenthe content of silicon-, phosphorus- and boron-containing polymerizedoxygen acid ions is little or when the interlayer water is removed by aheat treatment.

When a composition analysis is conducted, the molar ratio in the baselayers and total electric charge number of interlayer anions can bedetermined from analyzing metal cations in the basic layers; and fromanalyzing B anions, total electric charge number of B anions can bedetermined; and it becomes possible to predict presence or absence ofpolymerized oxygen acid ions in the silicon-, phosphorus- orboron-containing oxygen acid ions, based on the difference in themeasured electric charge numbers and the result of analysing silicon,phosphorus or boron.

According to infrared absorption spectrum analysis, when Si—O—Si linkageor P—O—P linkage are linearly present in the interlayer silicon- orphosphorus-containing polymerized oxygen acid ions, absorption isdetected in the spectrum at around 1250-1280 cm⁻¹.

Thus, by synthetically considering these analyses results, hydrotalcitecompound of the present invention is distinguishable from conventionalhydrotalcite compounds.

While the hydrotalcite compound of the invention exhibits gooddispersibility when it is blended with resin as it is, it may besurface-treated with at least one surface-treating agent of the groupconsisting of higher fatty acids; anionic surfactants; phosphoric acidesters; silane-, titanate- and aluminum-containing coupling agents; andfatty acid esters of polyhydric alcohols.

Specific examples of preferred surface-treating agents are as follows:higher fatty acids such as stearic acid, oleic acid, erucic acid,palmitic acid and lauric acid and alkali metal salts of these higherfatty acids; anionic surfactants such as sulfate esters of higheralcohols, eg., stearyl alcohol and oleyl alcohol, sulfate ester salts ofpolyethylene glycol ethers, amide bond sulfate ester salts, ether bondsulfonate salts, ester bond sulfonates, amide bond alkylallylsulfonatesalts and ether bond alkylallylsulfonate salts; phosphoric acid esterssuch as acid or alkali metal salts or amine salts, which are mono- ordiesters between orthophosphoric acid and oleyl alcohol, stearyl alcoholor the like, or mixtures of these esters; silane coupling agents such asvinylethoxysilane, γ-methacryloxypropyltrimethoxysilanevinyl-tris(2-methoxyethoxy)silane and γ-aminopropyltrimethoxysilane;titanate coupling agents such as isopropyl triisostearoyl titanate,isopropyl tris(dioctylpyrophosphate) titanate and isopropyltridecylbenzenesulfonyl titanate; and aluminum coupling agents such asacetalkoxyaluminum diisopropylate, etc.

As methods of the surface treatment, there are wet method and drymethod. In the wet method, a surface-treating agent as named above inliquid or emulsion state is added to slurry of the hydrotalcite compoundof the invention, and sufficiently mixed under stirring at a temperatureup to about 100° C. In the dry method, powder of the hydrotalcitecompound of the invention is put in a mixer such as a Henschel mixer, towhich the surface-treating agent in liquid, emulsion or solid state isadded and sufficiently mixed with or without heating. Preferably, thesurface-treating agent is used in an amount of about 0.1 to about 15% byweight of the hydrotalcite compound.

For use as an infrared absorbing agent either as it is or assurface-treated, the hydrotalcite compound of the invention preferablyhas an average secondary particle diameter as measured by laserdiffraction scattering method of not more than 5 μm and a BET specificsurface area of 30 m²/g or less, in consideration of mechanicalprocessability or dispersibility in resin. Also in terms of averageprimary particle diameter as observed with electron microscope, that ofthe hydrotalcite compound is preferably not more than 1 μm, inparticular, not more than 0.5 μm, inter alia, not more than 0.3 μm.Preferred configuration of the particles is platy (including hexagonalplaty form). Higher aspect ratio (average diameter of platyplane/average thickness) is preferred.

As examples of thermoplastic resins which are used for agricultural filmaccording to the invention, polyolefin resins, chlorine-containingresins, polyester resins, acrylic resins and fluorine-containing resinscan be named. Specific examples of the polyolefin resins includehomopolymers of α-olefins such as low-density, high-density or straightchain polyethylene and polypropylene; α-olefin copolymers such asethylene-propylene copolymers, ethylene-butene-1 copolymers,ethylene-4-methyl-1-pentene copolymers, ethylene-hexene copolymers andethylene-octene copolymers; and copolymers of α-olefins with monomersother than α-olefins, whose main component is the α-olefins, such asethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers,ethylene-methyl methacrylate copolymers, ethylene-vinyl acetate-methylmethacrylate copolymers and ionomer resins. As the catalyst to be usedin synthesizing these polyolefinic resins, for example,Ziegler-Natta-type catalyst, Cr-containing catalyst and single'site(metallocene) type catalyst may be named. Their synthesis method is notcritical, but any of solution methods or vapor phase methods under highpressure, reduced pressure or normal pressure may be used. Examples ofchlorine-containing resins include polyvinyl chloride, chlorinatedpolyvinyl chloride, polyvinylidene chloride, chlorinated polyethylene,vinyl chloride-vinyl acetate copolymers, vinyl chloride-ethylenecopolymers, vinyl chloride-styrene copolymers, vinylchloride-isobutylene copolymers, vinyl chloride-butadiene copolymers,vinyl chloride-isoprene copolymers, vinyl chloride-chlorinated propylenecopolymers, vinyl chloride-maleate copolymers, vinylchloride-methacrylate copolymers, vinyl chloride-acrylonitrilecopolymers, vinyl chloride-styrene-maleic anhydride copolymers, vinylchloride-styrene-acrylonitrile copolymers, vinyl chloride-vinylidenechloride-vinyl acetate copolymers and vinyl chloride-various vinyl ethercopolymers. Examples of polyester resins include polyethyleneterephthalate, polybutylene terephthalate, polybutylene naphthalate andpolyether polyesters; and those of fluorine-containing resins includepolytetrafluoroethylene and the like. Those resins can be used eithersingly or as a mixture of two or more of them.

The agricultural film according to the present invention may containvarious additives customary in this technology. Examples of suchadditives include light stabilizer, antihazing agent, antifogging agent,antioxidant, ultraviolet absorber, plasticizing agent, antistatic agent,lubricant, heat stabilizer, fluorescent agent, antiblocking agent,pigment, dyestuff, antibacterial agent, antimolding agent, partingagent, plate out-preventing agent-and processing aids. They may beconcurrently used with other infrared absorbing agent. By the concurrentuse of these various additives, agricultural film excelling inweatherability, anti-haze property, antifogging property, dustresistance, water repellence, toughness, resistance to agriculturalchemicals and to acid precipitation, heat resistance, antibleachingproperty, antibacterial and antifungicidal properties, stretchingprocessability and resistance to degradation of the resins caused byvarious additives, as well as in durability of those favorableproperties is obtained.

As the light stabilizers, for example, hindered amine compounds,cresols, melamines and benzoic acid may be named, hindered aminecompounds being frequently used in general. More specifically,2,2,6,6-tetraalkylpiperidine derivatives having a molecular weight notless than 250 and a substituent on 4-position are preferably used,examples of said 4-substituent including carboxylic acid groups, alkoxygroups and alkylamino groups. Their N-position may be substituted withan alkyl group. As specific examples of such hindered amine compounds,compounds of following formulae (a)-(t) and hindered amine-containingstabilizers such as Ciba Geigy's TINUVIN 492 and 494 may be named.

Such light stabilizers as above may be used singly or in combination ofmore than one, the amount of use being 0.02-5% by weight, preferably0.1-2% by weight, to the thermoplastic resin.

As antihazing agent, nonionic, anionic or cationic surfactants may beused, examples of which including polyoxyalkylene ethers, esters orpartial esters of polyhydric alcohols, esters or partial esters ofalkylene oxide adducts of polyhydric alcohols, higher alcohol sulfuricacid ester alkali metal salts, alkylarylsulfonates, quaternary ammoniumsalts and aliphatic amine derivatives. Specifically, polyoxyethylenelaurate, polyoxyethylene stearyl ether, polyoxyethylene nonyl phenylether, polyethylene glycol monopalmitate, polyethylene glycolmonostearate, polyoxyethylene sorbitan monolaurate, polyoxyethylenesorbitan monopalmitate; esters or partial esters of polyhydric alcoholssuch as glycerine, pentaerythritol, sorbitol, diglycerine andtriglycerine with aliphatic carboxylic acids such as lauric acid,palmitic acid, stearic acid and oleic acid; sodium lauryl sulfate,sodium dodecylbenzenesulfonate, sodium butylnaphthalenesulfonate,cetyltrimethylammonium chloride, alkyldimethylbenzylammonium chloride,dodecylamine hydrochloride, lauric acid laurylamidoethyl phosphate,triethylcetylammonium iodide, oleylaminodiethyl aminate and basicpyridinium salt of dodecylpyridinium sulfate may be named.

Use rate of such antihazing agent is 0.2-5% by weight, preferably 0.5-3%by weight, to the thermoplastic resin. Those antihazing agents as namedabove can be used either singly or in combination of two or more.

As antifogging agent, for example, fluorine compounds containingperfluoroalkyl groups or ω-hydrofluoroalkyl groups (fluorine-containingsurfactants) and silicon compounds having alkylsiloxane groups(silicon-containing surfactants) may be used.

Use rate of such antifogging agent is 0.01-5% by weight, preferably0.02-2% by weight, to the thermoplastic resin. Those antifogging agentsas named above can be used either singly or in combination of two ormore.

As antioxidant, phenol-, phosphorus-, sulfur- or hydroxyamine-containingantioxidants can be used. Those piperidine-containing compounds as namedamong the useful light stabilizers can also be used. Specific examplesof phenolic antioxidants include phenols such as2,6-di-tert-butyl-p-cresol,stearyl-(3,5-dimethyl-4-hydroxybenzyl)thioglycolate,stearyl-β-(4-hydroxy-3,5-di-tert-butylphenyl)propionate,distearyl-3,5-di-tert-butyl-4-hydroxybenzylphosfonate,2,4,6-tris(3′,5′-di-tert-butyl-4′-hydroxybenzylthio)-1,3,5-triazine,distearyl(4-hydroxy-3-methyl-5-tert-butyl)benzylmalonate,2,2′-methylenebis(4-methyl-6-tert-butylphenol),4,4′-methylenebis-(2,6-di-tert-butylphenol),2,2′-methylenebis[6-(1-methylcyclohexyl)-p-cresol],bis[3,5-bis(4-hydroxy-3-tert-butylphenyl)butyric acid] glycol ester,4,4′-butylidenebis(6-tert-butyl-m-cresol),2,2′-ethylidenebis(4,6-di-tert-butylphenol),1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,bis[2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl]terephthalate,1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butyl)benzylisocyanurate,1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene,2,6-diphenyl-4-octadecyloxyphenoltetraquis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane,1,3,5-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate,1,3,5-tris[(3,5-di-tert-butyl-4-hydroxyphenyl)-propionyloxyethyl]isocyanurate,2-octyl-4,6-di(4-hydroxy-3,5-di-tert-butyl)phenoxy-1,3,5-triazine and4,4′-thiobis(6-tert-butyl-m-cresol; and polyhydric phenol-carbonic acidoligoesters such as carbonic acid oligoesters of4,4′-butylidenebis(2-tert-butyl-5-methylphenol) (eg., those ofpolymerization degrees of 2, 3, 4, 5, 6, 7, 8, 9 and 10).

Specific examples of phosphorus-containing antioxidants include triarylphosphites such as triphenyl phosphite, tris(nonylphenyl)phosphite,tris(p-nonylphenyl)phosphite, tris(p-phenylphenyl)phosphite,tris(o-dicyclohexylphenyl)phosphite,tri(monononyl/di-nonylphenyl)phosphite, phenyl-p-nonylphenyl phosphite,tris(2,4-di-tert-butylphenyl)phosphite andtris[2-tert-butyl-4-(3-tert-butyl-4-hydroxy-5-methylphenylthio)5-methylphenyl]phosphite;alkylaryl phosphites such as mono-octyldiphenylphosphite,di-octylmonophenylphosphite, di-decylmonophenylphosphite andmonodecyl-phenylphenylphosphite; trialkyl phosphites such as tributylphosphite, trioctyl phosphite, tridecyl phosphite, trilauryl phosphiteand trioleyl phosphite; and organophosphoric acid-type ororganophosphoric acid metal salt-type compounds which are compounds oforganophosphoric acid metal salts containing alkyl, aryl, alkylarylgroups or ether linkages, such as di(tridecyl)-pentaerythritoldiphosphite, distearyl-pentaerythritol diphosphite,di(nonylphenyl)pentaerythriol diphosphite,bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite,bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite,tetra(tridecyl)isopropylidenediphenol diphosphite,hexa(tridecyl)-1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butanetriphosphite, tetraquis(2,4-di-tert-butylphenyl)biphenylenediphosphonite and 2,2′-methylenebis(4,6-di-tert-butylphenyl)(octyl)phosphite.

Examples of sulfur-containing antioxidants include dialkyl (such asdilauryl-, distearly)thiodipropionates and esters of alkylthiopropionicacids (such as butyl-, octyl-, lauryl- and stearyl-) with polyhydricalcohols (such as glycerine, trimethylolethane, trimethylolpropane,pentaerythritol, trishydroxyethyl isocyanurate). As specific examples,dilaurylthiodipropionate, distearylthiodipropionate and pentaerythritoltetralaurylthiopropionate may be named.

The use rate of such antioxidant is 0.01-5% by weight, preferably0.02-3% by weight, to the thermoplastic resin. These antioxidants can beused either singly or in combination of more than one.

Ultraviolet absorbing agents may be benzotriazole-, benzophenone- orsalicylate-type. Specific examples of benzotriazole ultravioletabsorbers include 2-(2′-hydroxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-5′-tert-butylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-dimethylphenyl)benzotriazole,2-(2′-methyl-4′-hydroxyphenyl)benzotriazole,2-(2′-hydroxy-3′-methyl-5′-tert-butylpheny)benzotriazole,(2′-hydroxy-3′,5′-di-tert-amylphenyl)benzotriazole,(2′-hydroxy-3′,5′-di-tert-butylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-dimethylphenyl-5-methoxybenzotriazole,2-(2′-n-octa-decyloxy-3′,5′-dimethylphenyl)-5-methylbenzotriazole,2-(2′-hydroxy-5′-methoxyphenyl)benzotriazole,2-(2′-bydroxy-4′-octoxyphenyl)benzotriazole,2-(2′-hydorxy-5′-methoxyphenyl)-5-methylbenzotriazole,2-(2′-hydroxy-5′-methoxyphenyl)-5,6-dichlorobenzotriazole,2-(2′-hydroxy-5′-tert-butylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-5′-phenylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-5′-dichlorohexylphenyl)benzotriazole,2-(2′-hydroxy-4′,5′-dichlorophenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′-methylphenyl)-5-butoxycarbonylbenzotriazole,2-(2′-hydroxy-4′,5′-dimethylphenyl)-5-butoxycarbonylbenzotriazole,2-(2′-hydroxy)-5-ethoxycarbonylbenzotriazole,2-(2′-acetoxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-5′-methylphenyl)-5-ethylsulfobenzotriazole,2-(2′-hydroxy-3′,5′-dimethylphenyl)-5-ethylsulfonbenzotriazole,2-(2′-hydroxy-5′-phenylphenyl)benzotriazole and2-(2′-hydroxy-5′-aminophenyl)benzotriazole.

Specific examples of benzophenone ultraviolet absorbers include2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octyloxybenzophenone,2-hydroxy-4-octoxybenzophenone, 2-bydroxy-4-n-dodecyloxybenzophenone,2-hydroxy-4-n-octadecyloxybenzophenone,2-hydroxy-4-benzyloxybenzophenone,2-hydroxy-4-methoxy-2′-carboxybenzophenone,2-hydroxy-4-methoxy-5-sulfobenzophenone, 2-hydroxy-5-chlorobenzophenone,2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxy-5-sulfobenzophenone and2,2′,4,4′-tetrahydroxybenzophenone.

Specific examples of salicylate ultraviolet absorbers include phenylsalicylate, p-tert-butylphenyl salicylate, p-methylphenyl salicylate andp-octylphenyl salicylate.

Besides the foregoing, triazine-type2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol or oxalicanilide type 2-ethoxy-2′-ethyl-oxalic bisanilide may also be named.

The use rate of such ultraviolet absorbers is 0.01-3% by weight,preferably 0.05-2% by weight, to the thermoplastic resin. The absorberscan be used either singly or in combination of two or more.

As plasticizers, those routinely used for plasticizing polyvinylchloride or olefin-vinyl alcohol copolymers can be used. For example,low molecular weight polyhydric alcohols, phthalic acid Aesters,phosphoric acid esters, aliphatic-basic acid esters, epoxy compounds andparaffins can be used.

Specific examples of the low molecular weight polyhydric alcoholsinclude glycerine, ethylene glycol, triethylene glycol and sorbitol.

Specific examples of phthalic acid ester plasticizers include dimethylphthalate, dibutyl phthalate, dioctyl phthalate, diisodecyl phthalate,heptyl phthalate, di-2-ethylhexyl phthalate, butylbenzyl phthalate,butyllauryl phthalate and methyloleyl phthalate.

Specific examples of phosphoric acid ester plasticizers includetricresyl phosphate, trixylenyl phosphate, dixylenyl monocresylphosphate, monoxylenyl cresyl phosphate, tributyl phosphate, triphenylphosphate and tri-2-ethylhexyl phosphate.

Specific examples of aliphatic-basic acid ester plasticizers includebutyl oleate, glycerine monooleate, butyl stearate, diisodecyl adipate,dibutyl adipate, dioctyl adipate, isodecyl adipate, dioctyl azelate,di-2-ethylhexyl adipate and methyl acetyl ricinoleate.

Specific examples of the epoxy compounds are similar to thoseexemplified as epoxy heat stabilizers later.

Specific examples of paraffinic plasticizers include chlorinatedparaffins, butylchlorinated paraffins and liquid paraffin.

Use rate of such plasticizers as above ranges 1-70% by weight,preferably 2-60% by weight, to the thermoplastic resin. They can be usedeither singly or in combination of two or more.

As useful antistatic agents, nonionic or cationic surfactants may benamed. Specific examples include polyethylene oxide, carbowax,pentaerythritol monostearate, sorbitol monopalmitate, polyoxyethylenealkylamine, polyglycol ether and sodium p-styrene-sulfonate.

Such antistatic agents are added in an amount of 0.01-5% by weight,preferably 0.02-3% by weight, to the thermoplastic resin. They can beused either singly or in combination of two or more.

As useful lubricants, aliphatic acid-, aliphatic acid amide- andester-type lubricants, waxes and paraffins can be named. Specificexamples include stearic acid, palmitic acid, myristic acid, stearicacid amide, palmitic acid amide, erucicacid amide,methylenebis-stearamide, ethylenebis-stearamide, butyl stearate, butylpalmitate, polyethylene wax and liquid paraffin.

Use rate of such lubricants ranges 0.01-5% by weight, preferably 0.05-3%by weight, to the thermoplastic resin. They can be used either singly orin combination of two or more.

As heat stabilizers, inorganic, organic acid metal salt-, organic acidcomplex metal salt-, organotin-, epoxy compound-, polyol-, sulfur-,organic antimony-, phosphite-, β-diketone-type and nitrogen-containingheat stabilizers can be used.

Specific examples of inorganic heat stabilizers include oxides,hydroxides, carbonates, sulfates, phophates, phosphites and silicates ofsuch metals as Li, Na, K, Mg, Ca, Sr, Ba, Pb, Zn, Cd, Zr, Al, Sn, Sb andBi; and salts of these metals with halogenated oxyacids such asperchloric acid, periodic acid, chloric acid, bromic acid, lodic acid,chlorous acid, hypochlorous acid and bromous acid.

As organic metal salt-type heat stabilizers, acidic, neutral or basicsalts of above-named metals with the below-exemplified organic acids canbe named: aliphatic carboxylic acids such as 2-ethylhexonic acid, lauricacids, myristic acid, palmitic acid, stearic acid, hydroxystearic acid,linoleic acid, behenic acid, isostearic acid, oleic acid, ricinoleicacid, caproic acid, heptanoic acid, n- or iso-octylic acid, pelargonicacid, capric acid, isodecanoic acid, undecylic acid, neotridecanoicacid, acetoacetic acid and acetic acid; dibasic acids such as maleicacid, thiodipropionic acid and dithiopropionic acid; partiallyesterified products of those dibasic acids with substituted orunsubstituted aliphatic, alicyclic or aromatic alcohols; and cyclicorganic acids such as benzoic acid, methylbenzoic acid, butylbenzoicacid, para-t-butylbenzoic acid, phenylacetic acid, salicylic acid,fumaric acid, naphthoic acid, abietic acid, phenylstearic acid,hydrinecarboxylic acid, cinnamic acid, rhodinic acid and haphthenicacid.

Specific examples of organic complex metal salt-type heat stabilizersinclude Ca/Zn, Ba/Cd, Ba/Zn and Ba/Cd/Zn salt systems of above organicacids.

Specific examples of organotin-type heat stabilizers include mono(ordi)methyl- or butyl- or octyl-tin-tri-(or di)laurate, mono(or di)methyl-or butyl- or octyl-tin maleate polymer, mono(or di)methyl-, or butyl- oroctyl-tin-tris(or bis)isooctyl maleate, mono(or di)methyl- or butyl- oroctyl-tin thioglycolate, mono(or di)methyl or butyl oroctyl-tin-2-mercaptopropionate, mono(or di)methyl or butyl- oroctyl-tin-tri(or di)dodecylmercaptide, mono(or di)methyl- or butyl- oroctyl-tin sulfide, mono(or di)methyl- or butyl- o roctyl-tin-thioglycolate, mono(or di)methyl- or butyl- oroctyl-tin-tris(or bis)2-mercaptoethyl oleate,thiobis(mono-methyltin-bis-2-mercaptoethyl oleate) and thiobis(dimethyl-or butyl- or octyl-tin-mono-2-mercaptoethyl oleate).

Specific examples of epoxy compound-type heat stabilizers includeepoxylated soybean oil, diacetomonoglycelide thereof, epoxylated linseedoil, epoxylated linseed oil fatty acid butyl, epoxylated1,2-polybutadiene, bisphenol-A-diglycidyl ether,3,4-epoxycyclohexylmethyl, 3,4-epoxycyclohexanecarboxylate, epoxylatedtallow oil, epoxylated cottonseed oil, epoxylated sunflower oil,epoxylated tall oil, epoxylated fish oil, epoxylated aceto-monoolefin,epoxylated stearic acid methyl-, -butyl, -isooctyl, -2-ethylhexyl,-isodecyl, -cyclohexyl, -dihydrononyl, -methyoxyethyl, -acetoxyethyl,-benzoyl, -tetrahydrofuryl, -phenyl or -p-tert-butylphenyl, epoxylatedtall oil fatty acidbutyl, -n-octyl, -isooctyl or -2-ethylhexyl,epoxytriacetomonoricinoleic acid glyceride, 9,10-epoxystearic acid esterof 3,4-epoxycyclohexylmethanol, 9,10,12,13-diepoxystearic acid ester of3,4-epokycyclohexylmethanol, 2-ethyl-1,3-hexanediol ester of3,4-epoxycyclohexylcarboxylic acid, dialkyl (eg., di-n-butyl,di-n-hexyl, di-2-ethylhexyl, diisooctyl, di-n-decyl, diisodecyl,di-n-butyldecyl and the like) esters of epoxyhexahydrophthalic acid,3,4-epoxy-6-methylcyclohexyl carboxylate,bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate and condensation productof epihalohydrin and bisphenol A.

Specific examples of polyol-type heat stabilizers includepentaerythritol, mannitol, xylitol, sorbitol, glycerine,trimethylolpropane, polyethylene glycol, polyvinyl alcohol,1,3-butanediol, propylene glycol, dipropylene glycol, ethylene glycol,diethylene glycol, neopentyl glycol, triethylolmethane, diglycerine,di-trimethylolpropane, di-tri-methylol ethane, di-, tri- ortetra-pentaerythritol, tris(hydroxyethyl)isocyanurate; and partialesters of these polyols with such organic acids as aliphatic carboxylicacids, aromatic carboxylic acids, amino acids and oxyacids. Specificexamples of the organic acids which form the partial esters includemonovalent aliphatic carboxylic acids such as octylic acid, lauric acid,myristic acid, palmitic acid, stearic acid, isostearic acid,hydroxystearic acid, oleic acid and ricinoleic acid; divalent aliphaticcarboxylic acids such as malonic acid, succinic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,phthalic acid, maleic acid, fumaric acid, itaconic acid, thiodipropionicacid and dithiopropionic acid; aromatic carboxylic acids such as benzoicacid, methylbenzoic acid and salicylic acid; amino acids such asglycine, alanine, leucine, phenylalanine, methionine, aspartic acid,glutamic acid and lysine; and oxy acids such as lactic acid, citricacid, tartaric acid and malic acid.

Specific examples of sulfur-type heat stabilizers includethiodipropionic acid esters such as dilaurylthiodipropionate,distearylthiodipropionate and laurylstearylthiodipropionate;triazinethiols such as 6-enilino-1,3,5-triazine-2,4-dithiol; andthiolcarboxylic anhydride such as thiollauric anhydride.

Specific examples of organic antimony-type heat stabilizers includemono(or di)alkylantimony laurates such as mono(or di)methyl-, butyl- oroctyl-antimony tri(or di)laurate; mono(or di)alkyl antimony maleatessuch as mono(or di)methyl-, butyl- or octyl-antimony maleate polymersand mono(or di)methyl-, butyl- or octylantimony tris(or bis)isooctylmaleate; and mono(or di)alkylantimony mercaptides such as mono(ordi)methyl-, butyl- or octyl-antimonytris(or bis)isooctylthioglycolate,mono(or di)methyl-, butyl- or octylantimony-tri(or bis)thioglycolate (or2-mercaptopropionate), mono(or di)methyl-, butyl- oroctyl-antimony-tri(or di)dodecylmercaptide, mono(or di)methylantimonysulfide, dioctylantimony sulfide, didodecylantirmony sulfide, mono(ordi)methyl-, butyl- or octylantimony-tris(or bis)-2-mercaptoethyl oleate,thiobis[monomethylantimony-bis(2-mercaptoethyl oleate)] andthiobis[dimethyl-, butyl- or octyl-antimony-bis(2-mercaptoethyloleate)].

As phosphite-type heat stabilizers, those exemplified as phosphorusantioxidants can be used.

Specific examples of β-diketone heat stabilizers include ethylacetoacetate, dehydroacetic acid, acetylacetone, benzoylacetone,benzoylpropionylmethane, dibenzoylmethane, stearoylbenzoylmethane,trifluoroacetylacetone, dehydropropionylacetic acid,dehydrobenzoylacetic acid, cyclohexane-1,3-dione, dimethone,2,2-methylenecyclohexan-1,3-dione, 2-benzylcyclohexan-1,3-dione,acetyltetralone, palmitoyltetralone, stearoyltetralone,benzoyltatralone, 2-acetylcyclohexanone, 2-benzoylcyclohexanone,2-acetylcyclohexan-1,3-dione, benzoyl-p-chlorobenzoylmethane,bis(4-methylbenzoyl)methane, bis(2-hydroxybenzoyl)methane,benzoylacetylmethane, tribenzoylmethane, diacetylbenzoylmethane,palimitoylbenzoylmethane, lauroylbenzoylmethane,4-methoxybenzoylbenzoylmethane, bis(4-methoxybenzoyl)methane,bis(4-chlorobenzoyl)methane, bis(3,4-methylenedioxybenzoyl)methane,benzoylacetyl-octylmethane, benzoylacetylphenylmethane,stearoyl-4-methoxybenzoylmethane, bis(4-tert-butylbenzoyl)methane,benzoylacetylethylmethane, benzoyltrifluoroacetylmethane,diacetylmethane, butanoylacetylmethane, heptanoylacetylmethane,triacetylmethane, distearoylmethane, stearoylacetylmethane,palmitoylacetylmethane, lauroylacetylmethane, benzoylformylmethane,acetylformylmethane, benzoylphenylacetylmethane,bis(cyclohexanoyl)methane and dipivaloylmethane; and metal salts ofthese compounds with such metals as Li, Na, Mg, Ca, Ba, Sr, Zn, Al, Zrand Sn.

Specific example of nitrogen-containing heat stabilizers includediphenylthiourea; P-aminocrotonic acid esters of such alcohols asstearyl alcohol, cetyl alcohol, 1,3-butanediol and thiodiethyleneglycol; and 2-phenylindole anddihydro-1,4-dimethyl-2,6-dicarbodidecyloxy-3,5-pyridine.

Use rate of those heat stabilizers ranges 0.001-10% by weight,preferably 0.005-5% by weight, to the thermoplastic resin. They can beused either singly or in combination of two or more.

Flourescent agents may also be added to the agricultural film of thepresent invention.

As the fluorescent agents, those of violanthrone, isoviolanthrone,perylene, thioxanthene, coumarin, anthraquinone, benzopyran,naphthalimide, or naphthalic acid, benzopiperidine, pyrazine,cyanopyrazine, stilbene, diaminodiphenyl, imidazole, imidazolone,triazole, thiazole, oxazole, carbostyril, pyrazoline and dihydropyridinecompounds can be named.

Use rate of such flourescent agents ranges 0.001-10% by weight,preferably 0.01-5% by weight, to the thermoplastic resin. They can beused either singly or in combination of two or more.

Finally, as examples of other infrared absorbing agents, silica andsilicate; hydroxide, oxide, aluminate, borate and sulfate of lithium,calcium, magnesium and aluminium; and conventional hydrotalicitecompounds may be named. They can be used either singly or in combinationof two or more. Whereas, because the hydrotalcite compound of thepresent invention holding the A anions and B anions exhibits excellentinfrared absorbing ability and is capable of imparting excellent lighttransmission to an agricultural film which contains said compound, it ispreferably used as an infrared absorbing agent by itself. Suitableamount of an infrared absorbing agent, in terms of either thehydrotalcite compound of the present invention alone or that incombination with other infrared absorbing agent or agents, is 1-30% byweight to, for example, the thermoplastic resin which constituents theobject agricultural film. Where the amount is less than 1% by weight,its effect as infrared absorbing agent cannot be sufficiently exhibited,and when it exceeds 30% by weight, it impairs ultraviolet and visiblelight transmission as well as mechanical strength of the agriculturalfilm.

When such problems as foaming or fish eye formation occur in theoccasion of incorporating the hydrotalcite compound of the invention asan infrared absorbing agent into an agricultural film-formingthermoplastic resin, or in the occasion of film-molding, if necessarythe hydrotalcite compound from which the interlayer water (water ofcrystallization) has been removed can be used.

The incorporation or kneading can be conducted according to the acceptedpractice. For example, the resin, infrared absorbing agent and otheradditives are mixed with, e.g., a Henschel mixer, super mixer, ribbonblender and the like, and then melted and kneaded in a Bumbury's mixer,kneading extruder, pressure kneader or the like. The kneaded productthen can be formed into film by conventional molding methodes such as,for example, inflation molding or extrusion T-die film-molding method.

The agricultural film of the present invention can be either monolayeredor multilayered. As the construction of the multilayered film, forexample, single composition-2 layers, single composition-3 layers, 2compositions-2 layers, 2 compositions-3 layers, 3 compositions-3 layers,3 compositions-4 layers, 3 compositions-5 layers, 4 compositions-4layers, 4 compositions-5 layers, 5 compositions-5 layers can be used.Kind of thermoplastic resin or resin blend may be different amongindividual layers. Of useful thermoplastic resins, it is desirable toselect at least one resin which shows favorable absorption at thewavelength region of 2.5 μm-25 μm, because of good heat insulation.Again, additives for individual layers can be suitably selectedaccording to the intended functions thereof, to formulate the optimumblend for each layer. It is also possible to form an antihazing film onat least the inner surface of the agricultural film which is to bestretched over agricultural greenhouses or the like for the purpose ofmaintaining antihazing performance of the film over many hours, besidesthe earlier described method of blending an antihazing agent in thefilm.

Hereinafter the present invention is further explained referring toExamples and Comparative Examples, it being understood that theinvention is not thereby limited.

Each hydrotalcite compound made in Examples or Comparative Examples wasfirst identified by means of X-ray diffractiometry (XRD). Then molarratios in its base layers (x, y₁ and y₂) were calculated based onanalysis of metal cations by composition analysis method, and the molarratio (z₂) of B anions to the base layers, based on analysis of the Banions. The ratio of total electric charge number of B anions in thetotal electric charge number (x) which is determined depending on thebase layers is calculated by substituting the so determined values forz₂ and x in the formula (total electric charge number of (B)z2)/x). Asto the silicon-, phosphorus- and boron-containing oxygen acid ions whichare A anions, whether or not those A anions held at interlayer containsilicon-, phosphorus- and boron-containing polymerized oxygen acid ionsis estimated, based on the starting materials which were used in theoccasion of ion-exchange, analysis values of Si, P or B found upon thecomposition analysis, spacing at (002) or (003) planes determined byXRD, and. the result of infrared absorption spectrometory. It isdifficult to judge in what form or forms such silicon-, phosphorus- andboron-containing oxygen acid ions are held in the interlayer.Furthermore, these oxygen acid ions include those containing single Hradical or OH radical or plurality of those radicals and alsopolymerized oxygen acid ions differing in degree of polymerization, andit is difficult to specify their electric charges. In the followingExamples, therefore, compositions of silicon-, phosphorus- andboron-containing oxygen acid ions are conveniently expressed as:(polymerized (Si_(m)O_(2m+1)), (polymerized P_(m)O_((5m/2)+1)) and(polymerized B_(m)O_((3m/2)+1)), which are invariably assumed to have anelectric charge of 2⁻ each in calculating the composition formulae.Furthermore, molar ratios of Si, P or B to Al are calculated bysubstituting the respective composition values in the formula (molnumber of Si+P+B)/(mol number of Al₂O₃). Specific surface areas aregiven by the numerical values as determined by BET process from theadsorbed amounts of nitrogen gas. The average secondary particlediameters are the numerical values obtained by adding each powder to anorganic solvent, subjecting the system to an ultrasonic dispersion andthen measuring the particle diameters by laser diffractive scatteringmethod.

In respect of those films containing the infrared absorbing agents asprovided by Examples and Comparative Examples, dispersibility of theagents in the films, heat insulation index, total light transmission andhaze value (degree of haziness) were measured. The dispersibility ofeach infrared absorbing agent in the respective film (formation of whiteblisters) was evaluated by visual observation.

The heat insulation indices were calculated by a method described later,from the measurements of infrared absorption at individual wavelengthsusing infrared absorption spectrum measuring device. Also lighttransmission was measured with hazemeter, and the result was expressedas total light transmission and haze value (degree of haziness).

The heat insulation index was calculated as follows. The black bodyradiation energy (Eλ·dλ) at each wavelength was determined by theequation (3) below, and the total black body radiation energy density,by integrating the black body radiation energy levels from 400 cm⁻¹ to2,000 cm⁻¹ (ΣEλ·dλ). Then infrared absorption of each film (containingan infrared absorbing agent) at each wavelength was measured withinfrared absorption spectrum-measuring device, and by multiplying theblack body radiation energy (EA dX) at each wavelength by the infraredabsorption at the same wavelength and integrating the products, totalabsorption energy density of the film was determined. The ratio of thetotal black body radiation energy density to the total absorption energydensity of the film [following equation (6)] is indicated as the heatinsulation index.

Eλ·dλ=2πhC{circumflex over ( )}2/[λ{circumflex over ( )}5{e{circumflexover ( )}(hC/λkT)−1}]·dλ  (3)

λ: wavelength

h: Planck's constant

C: velocity of light in vacuum

k: Boltzmann's constant

T: absolute temperature.

Heat insulation index=(total absorption energy density/total black bodyradiation energy density)×100  (6)

A higher heat insulation index as calculated from the above equationsignifies greater infrared absorbability, i.e., higher heat insulationproperty. Also the closer the total light transmission to 100 asmeasured by hazemeter, the better the visible light transmission of thefilm, and the less the haze value (degree of haziness), the less thehaziness in the film.

EXAMPLE 1

A liquid mixture of 2 liters of 1.5 mols/liter MgCl₂ solution and 0.667liter of 1.0 mol/liter Al₂(SO₄)₃ solution was put in a stainless steelvessel, and into which 2.889 liters of 3.0 mols/liter NaOH solution waspoured under stirring, followed by about 30, minutes' stirring. Theresulting reaction slurry was transferred into an autoclave, subjectedto a hydrothermal treatment at 170° C. for 6 hours, cooled, filtered andwashed with water. Then the de-watered product was thrown into astainless steel vessel containing 5 liters of ion-exchange water, onceagain converted to a slurry under stirring and heated to 90° C. Undercontinued stirring, 1.300 liters of 1.0 mol/liter (as SiO₂) sodiumsilicate (No. 3 water glass) solution was added, followed by further 2hours' stirring. Finally the system was filtered, and the recoveredsolid was washed with water and dried at 95° C. for one day and night.So dried product was pulverized to provide the product sample.

Upon analysis, the composition of the product was:

Mg_(0.692)Al_(0.308)(OH)₂ (polymerizedSi_(4.84)O_(10.68))_(0.062)(SO₄)_(0.062)(CO₃)_(0.030). 0.69H₂O. Theratio of B anions to the total electric charge (x) was 0.60, the molarratio of Si to Al₂O₃ was 1.95, the BET specific surface area of thepowder was 23 m²/g, and the average secondary particle diameter was 0.69μm.

EXAMPLE 2

The procedures up to the sodium silicate treatment of Example 1 wererepeated, followed by filtration and the recovered solid was washed withwater and de-watered. The product was thrown into a stainless steelvessel containing 5 liters of ion-exchange water, re-slurried understirring and heated to 80° C. Separately, 16.5 g of sodium stearate(purity: 86%) was weighed and dissolved in ion-exchange water at 80° C.,and the. solution was poured into the slurry under stirring, to effect asurface treatment. Finally the system was filtered, washed with water,dried for a day and night at 95° C., and pulverized to provide theproduct sample.

Upon analysis, the composition of the product was identified to be:

Mg_(0.692)Al_(0.308)(OH)₂ (polymerizedSi_(4.84)O_(10.68))_(0.062)(SO₄)_(0.062)(CO₃)_(0.030). 0.69H₂O. Theratio of B anions in the total electric charge (x) was 0.60, the molarratio of Si to Al₂O₃ was 1.95, the BET specific surface area of thepowder was 18 m²/g, average secondary particle diameter was 0.77 μm andthe adsorption of the surface treating agent was 3.0% by weight.

EXAMPLE 3

The product of Example 2 was further heat-treated at 200° C. for 3 hoursto be removed of its interlayer water.

Upon analysis, the composition of the product was identified to be:

Mg_(0.062)Al_(0.308)(OH)₂ (polymerizedSi_(4.84)O_(10.68))_(0.062)(SO₄)_(0.062)(CO₃)_(0.030). 0.09H₂O. Theratio of B anions in the total electric charge (x) was 0.60, the molarratio of Si to Al₂O₃ was 1.95, the BET specific surface area of thepowder was 20 m²/g, average secondary particle diameter was 0.72 μm andthe adsorption of the surface treating agent was 3.3% by weight.

EXAMPLE 4

Two liters of 1.5 mols/liter MgCl₂ solution and 0.750 liter of 1.0mol/liter Al₂(SO₄)₃ solution were fed into a stainless steel vessel, andinto which 3.000 liters of 3.0 mols/liter NaOH solution was poured,followed by about 30 minutes' stirring. Then the reaction slurry wastransferred into an autoclave, given a hydrothermal treatment at 170° C.for 6 hours, cooled to not higher than 100° C. and transferred into astainless steel vessel. Re-heating the slurry to 80° C., 1.125 liters of1.0 mol/liter (as SiO₂) sodium silicate solution (No. 3 water glass) wasadded to the slurry under stirring, followed by an hour's stirring.Separately, 14 g of stearyl phosphate (purity: 99%) was weighed andsuspended in diluted sodium hydroxide solution at 80° C. The suspensionwas poured into the slurry to effect a surface treatment. Finally thesystem wasp filtered, and the recovered solid was washed with water,dried for a day and night at 95° C., and pulverized to provide theproduct sample.

Upon analysis, the composition of the product was identified to be:

Mg_(0.667)Al_(0.333)(OH)₂ (polymerizedSi_(6.02)O_(13.04))_(0.0415)(SO₄)_(0.095)(CO₃)_(0.030). 0.43H₂O. Theratio of B anions in the total electric charge (x) was 0.75, the molarratio of Si to Al₂O₃ was 1.50, the BET specific surface area of thepowder was 15 m²/g, average secondary particle diameter was 0.70 μm, andadsorption of the surface treating agent was 3.0% by weight.

EXAMPLE 5

The product of Example 4 was further heat-treated at 200° C. for 3 hoursto be removed of the interlayer water.

Upon analysis, the composition of the product was identified to be:

Mg_(0.667)Al_(0.333)(OH)₂ (polymerizedSi_(6.02)O_(13.04))_(0.0415)(SO₄)_(0.095)(CO₃)_(0.030). 0.08H₂O. Theratio of B anions in the total electric charge (x) was 0.75, the molarratio of Si to Al₂O₃ was 1.50, the BET specific surface area of thepowder was 18 m²/g, average secondary particle diameter was 0.68 μm andthe adsorption of the surface treating agent was 3.3% by weight.

EXAMPLE 6

Two liters of 1.5 mols/liter MgCl₂ solution and 0.698 liter of 1.0mol/liter Al₂(SO₄)₃ solution were put in a stainless steel vessel, andinto which 2.930 liters of 3.0 mols/liter NaOH solution was poured understirring, followed by 30 minutes' stirring. The resulting reactionslurry was transferred into an autoclave, subjected to a hydrothermaltreatment at 170° C. for 6 hours, cooled, filtered and washed withwater. Then the de-watered product was thrown into a stainless steelvessel containing 5 liters of ion-exchange water and heated to 90° C.Then 1.605 liters of 1.0 mol/liter (as SiO₂) sodium silicate (No. 3water glass) solution was added under stirring, and the stirring wascontinued for further 3 hours. Separately, 18.6 g of stearyl phosphate(purity: 99%) was weighed and suspended in diluted sodium hydroxidesolution at 90° C. The suspension was poured into the slurry understirring to effect a surface treatment. Finally the system was filtered,and the recovered solid was washed with water and dried for a day andnight at 95° C., and pulverized to provide the product sample, which wasfurther heat-treated at 200° C. for 3 hours to be removed of theinterlayer water.

Upon analysis, the composition of the product was identified to be:

Mg_(0.683)Al_(0.317)(OH)₂ (polymerizedSi_(4.26)O_(9.52))_(0.0855)(SO₄)_(0.050)(CO₃)_(0.023). 0.11H₂O. Theratio of B anions in the total electric charge (x) was 0.46; the molarratio of Si to Al₂O₃ was 2.30, the BET specific surface area of thepowder was 19 m²/g, average secondary particle diameter was 0.62 μm andthe adsorption of the surface treating agent was 4.3% by weight.

EXAMPLE 7

Three liters of 2.0 mols/liter Mg(OH)₂ slurry was put in a stainlesssteel vessel and to which 0.750 liter of 2.0 mols/liter Al(NO₃)₃solution was added under stirring, followed by about 30 minutes'stirring. The resulting reaction slurry was transferred to an autoclaveand given a hydrothermal treatment at 170° C. for 10 hours. Aftercooling, filtering and washing the recovered solid with water, thede-watered product was thrown into a stainless steel vessel containingion-exchange water. Into the vessel, 2.100 liters of 1.0 mol/liter (asSiO₂) sodium silicate (No. 3 water glass) solution was added, followedby heating to 90° C. and stirring for 2 hours. Separately, 17.8 g ofstearyl phosphate (99%) was weighed and suspended in diluted sodiumhydroxide solution at 90° C., and the suspension was poured into theslurry to effect a surface treatment. Finally the system was filtered,and the recovered solid was washed with water and dried at 95° C. forone day and night. So dried product was pulverized to provide theproduct sample, which was further heat-treated at 200° C. for 3 hours tobe removed of the interlayer water.

Upon analysis, the composition of the product was identified to be:

Mg_(0.750)Al_(0.250)(OH)₂ (polymerizedSi_(3.17)O_(7.34))_(0.115)(NO₃)_(0.005)(CO₃)_(0.012). 0.06H₂O. The ratioof B anions in the total electric charge (x) was 0.12, the molar ratioof Si to Al₂O₃ was 2.80, the BET specific surface area of the powder was16 m²/g, average secondary particle diameter was 0.68 μm and theadsorption of the surface treating agent was 3.3% by weight.

EXAMPLE 8

The procedures up to the hydrothermal treatment of Example 1 wererepeated using identical starting materials, and the resulting slurrywas cooled, filtered and washed with water. Then the de-watered productwas thrown into a stainless steel vessel containing 5 liters ofion-exchange water, stirred, re-slurried, and heated to 90° C. Understirring, 0.967 liter of 1.0 mol/liter (as SiO₂) sodium silicate (No. 3water glass) solution and 0.333 liter of 1.0 mol/liter (as SiO₂) sodiummetasilicate solution were added to the slurry, followed by 2 hours'stirring. While continuing the stirring, 21.6 g of sodium stearate(purity: 86%) was separately weighed and dissolved in ion-exchange waterat 90° C., and the solution was poured into the slurry under continualstirring to effect a surface treatment. Finally the system was filteredand the recovered solid was washed with water, dried for a day and nightat 95° C. and pulverized to provide the product sample. The same productwas further heat-treated at 200° C. for 3 hours to be removed of theinterlayer water.

Upon analysis, the composition of the product was identified to be:

Mg_(0.692)Al_(0.308)(OH)₂ (polymerized and monomericSi_(3.37)O_(7.74))_(0.089)(SO₄)_(0.024)(CO₃)_(0.040). 0.09H₂O. The ratioof B anins in the total electric charge (x) was 0.42, the molar ratio ofSi to Al₂O₃ was 1.95, the BET specific surface area of the powder was 18m²/g, average secondary particle diameter was 0.77 μm and the adsorptionof the surface treating agent was 4.4% by weight.

EXAMPLE 9

The procedures up to the hydrothermal treatment of Example 1 wererepeated using identical starting materials, and the resulting slurrywas cooled, filtered and washed with water. Then the de-watered productwas thrown into a stainless steel vessel containing ion-exchange water,stirred and re-slurried, heated to 80° C. Under stirring, 1.233 litersof 1.0 mol/liter KH₂PO₄ solution was added to the slurry, followed by anhour's stirring. Separately, 22.3 g of sodium stearate (purity: 86%) wasweighed and dissolved in ion-exchange water at 80° C., and the solutionwas poured into the slurry under continual stirring to effect a surfacetreatment. Finally the system was filtered and the recovered solid waswashed with water, dried for a day and night at 95° C. and pulverized toprovide the product sample. The same product was further heat-treated at200° C. for 3 hours to be removed of the interlayer water.

Upon analysis, the composition of the product was identified to be:

Mg_(0.692)Al_(0.308)(OH)₂ (polymerized P_(3.31)O_(9.275))₀₀₈₆(SO₄)_(0. 020)(CO₃)_(0.048). 0.09H₂O. The ratio of Banions in the total electric charge (x) was 0.44, the molar ratio of Pto Al₂O₃ was 1.85, the BET specific surface area of the powder was 23m²/g, average secondary particle diameter was 0.57 μm and the surfacetreating agent's adsorption was 4.4% by weight.

EXAMPLE 10

A liquid mixture was prepared by mixing 4 liters of 1.5 mols/liter MgCl₂solution and 1.396 liters of 1.0 mol/liter Al₂(SO₄)₃ solution. Also 1.0mol/liter sodium carbonate solution and 2.0 mols/liter NaOH solutionwere prepared. The liquid mixture and the sodium carbonate solution werecontinuously poured into a continuous reaction vessel containingion-exchange water, at a flow rate of 100 ml/min. and 20 ml/min.,respectively, while simultaneously adding the NaOH solution to maintainthe reaction pH at 8-10. The residence time was about 20 minutes. Afterconcentration of the reaction product into the slurry became stable,about 5.85 liters of the slurry was sampled, which slurry was filtered,washed with about 2 liters of 0.5 mol/liter sodium carbonate solution,washed with water and suspended in 4.5 liters of ion-exchange water. Theresulting slurry was transferred into an autoclave and subjected to ahydrothermal treatment at 170° C. for 12 hours. After cooling, theresulting slurry was transferred into a stainless steel vessel, and intowhich 0.928 liter of 1.0 mol/liter H₃PO₄ solution was added understirring, stirred for an hour and then heated to 80° C. Separately, 10.3g of sodium laurate (purity: 99%) was weighed and dissolved inion-exchange water at 80° C., and the solution was added to the slurryunder continual stirring to effect a surface treatment. Finally thesystem was filtered, washed with water, dried for a day and night at 95°C., and pulverized to provide the product sample which was furtherheat-treated at 200° C. for 3 hours to be removed of its interlayerwater.

Upon analysis, the composition of the product was identified to be:

Mg_(0.0683)Al_(0.317)(OH)₂ (polymerizedSi_(1.89)O_(5.725))_(0.1115)(CO₃)_(0.047). 0.11H₂O. The ratio of Banions in the total electric charge (x) was 0.30, the molar ratio of Pto Al₂O₃ was 1.33, the BET specific surface area of the powder was 20m²/g, the average secondary particle diameter was 0.43 μm and theadsorption of the surface treating agent was 2.3% by weight.

EXAMPLE 11

The procedures up to the hydrothermal treatment of Example 1 wererepeated using identical starting materials, and the resulting slurrywas cooled, filtered and washed with water. Then the de-watered productwas thrown into a stainless steel vessel containing ion-exchange water,stirred and re-slurried and heated to 90° C. Under stirring, 0.647 literof 1.0 mol/liter (as SiO₂) sodium silicate (No. 3 water glass) solutionand 0.647 liter of 1.0 mol/liter KH₂PO₄ solution were added understirring, followed by further 2 hours' stirring. Separately, 19.2 g ofsodium stearate (purity: 86%) was weighed and dissolved in ion-exchangewater at 90° C., and the solution was added to the slurry undercontinued stirring to effect a surface treatment. Finally the system wasfiltered, washed with water, dried at 95° C. for a day and night, andpulverized to provide a product sample. The product was heat-treated at200° C. for 3 hours to be removed of the interlayer water.

Upon analysis, the composition of the product was identified to be:

Mg_(0.692)Al_(0.308)(OH)₂ (polymerized Si_(3.36)O_(7.72))_(0.0445)(polymerized P_(3.36)O_(9.40))_(0.0445)(SO₄)_(0.042)(CO₃)_(0.023).0.11H₂O. The ratio of B anion the total electric charge (x) was 0.42;the molar ratio of Si to Al₂O₃ was 0.97, that of P to Al₂O₃ was 0.97,the BET specific surface area of the powder was 20 m²/g, averagesecondary particle diameter was 0.80 μm and the adsorption of thesurface treating agent was 3.9% by weight.

EXAMPLE 12

A liquid mixture of 1.75 liters of 1.5 mols/liter MgCl₂ solution, 0.25liter of 1.5 mols/liter ZnCl₂ solution and 0.75 liter of 1.0 mol/literAl₂(SO₄)₃ solution was put in a stainless steel vessel, and to which3.000 liters of 3.0 mols/liter NaOH solution was poured under stirring,followed by 30 minutes' stirring. The reaction slurry was transferredinto an autoclave and given a hydrothermal treatment at 150° C. for 10hours. The slurry was cooled, filtered and washed with water and thede-watered product was thrown into a stainless steel vessel containingion-exchange water, stirred and re-slurried. The slurry was heated to90° C., and into which 0.469 liter of 1.0 mol/liter sodium tetraborate(Na₂B₄O₇.10H₂O) solution was added under stirring, followed by 2 hours'stirring. Separately, 20.9 g of sodium stearate (purity: 86%) wasweighed and dissolved in 90° C. ion-exchange water and the solution waspoured into the slurry under continued stirring, to effect a surfacetreatment. Finally the system was filtered and the recovered solid waswashed with water, dried for a day and night at 95° C. and pulverized toprovide the product sample. The same product was further heat-treated at200° C. for 3 hours to be removed of the interlayer water.

Upon analysis, the composition of the product was identified to be:

(Mg_(0.875)Zn_(0.125))_(0.067)Al_(0.033)(OH)₂ (polymerizedB_(4.40)O_(7.60))_(0.0945)M(SO₄)_(0.040)(CO₃)_(0.032). 0.07H₂O. Theratio of B anions in the total electric charge (x) was 0.43; the molarratio of B to Al₂O₃ was 2.50, the BET specific surface area of thepowder was 16 m²/g, average secondary particle diameter was 0.66 μm andthe adsorption of the surface treating agent was 4.5% by weight.

EXAMPLE 13

A liquid mixture of 1.10 liters of 1.0 mol/liter Li₂SO₄ solution and2.00 liters of 1.0 mol/liter Al₄(SO₄)₃ solution was put in a stainlesssteel vessel, and into which 4.00 liters of 3.0 mols/liter NaOH solutionwas poured under stirring, followed by about 30 minutes' stirring. Theresulting reaction slurry was transferred into an autoclave, subjectedto a hydrothermal treatment at 170° C. for 6 hours, cooled, filtered andwashed with water. Then the de-watered product was thrown into astainless steel vessel containing ion-exchange water and heated to 90°C., into which then 1.960 liters of 1.0 mol/liter (as SiO₂) sodiumsilicate (No. 3 water glass) solution was added under stirring, followedby further 3 hours' stirring. Separately, 23.3 g of stearyl phosphate(purity: 99%) was weighed and suspended in 90° C. diluted sodiumhydroxide solution. The suspension was poured into the slurry to effecta surface treatment. Finally the system was filtered, and the recoveredsolid was washed with water and dried for one day and night. So driedproduct was pulverized to provide the product sample, which was furtherheat-treated at 200° C. for 3 hours to be removed of the interlayerwater.

Upon analysis, the composition of the product was:

Li_(0.97)Al₂(OH)₆ (polymerizedSi_(2.49)O_(5.98))_(0.393)(SO₄)_(0.752)(CO₃)_(0.017). 0.50H₂O. The ratioof B anions in the total electric charge (x) was 0.19, the molar ratioof Si to Al₂O₃ was 0.98, the BET specific surface area of the powder was19 m²/g, and the average secondary particle diameter was 1.00 μm and thesurface treating agent's adsorption was 4.5% by weight.

EXAMPLE 14

A liquid mixture of 1.10 liters of 1.0 mol/liter Li₂SO₄ solution, 0.04liter of 1.0 mol/liter MgCl solution and 2.00 liters of 1.0 mol/literAl₂(SO₄)₃ solution was put in a stainless steel vessel, and into which4.00 liters of 3.0 mols/liter NaOH solution was poured under stirring,followed by 30 minutes' stirring. Then the reaction slurry wastransferred into an autoclave and given a hydrothermal treatment at 170°C. for 6 hours, cooled, filtered and washed with water. Then thede-watered product was thrown into a stainless steel vessel containingion-exchange water and heated to 90° C., into which then 2.00 liters of1.0 mol/liter KH₂PO₄ solution was added under stirring, followed byfurther 3 hours' stirring. Separately, 29.6 g of sodium stearate(purity: 86%) was weighed and dissolved in 90° C. ion-exchange water,and the solution was poured into the slurry to effect a surfacetreatment. Finally the system was filtered, washed with water, dried fora day and night at 95° C., and pulverized to provide the product samplewhich was further heat-treated at 200° C. for 3 hours to be removed ofthe interlayer water.

Upon analysis, the composition of the product was identified to be:

Li_(0.95)Mg_(0.02)Al2(OH)₆ (polymerizedP_(2.21)O_(6.53))_(0.444)(SO₄)_(0.035)(CO₃)_(0.017). 0.60H₂O. The ratioof B anions to the total electric charge (x) was 0.11, the molar ratioof P to Al₂O₃ was 0.98, the BET specific surface area was 18 m²/g,average secondary particle diameter was 0.77 μm and the adsorption ofthe surface treating agent was 4.4% by weight.

COMPARATIVE EXAMPLE 1

DHT-4A (manufactured by Kyowa Chemical Industries) which is a Mg—Alhydrotalcite compound having carbonate ions in its interlayer and whichis currently widely used as an infrared absorbing agent in the field ofagricultural film was used as the reference agent.

Upon analysis, it had a composition of

M_(0.683)Al_(0.317)(OH)₂(CO₃)_(0.158).0.56H₂O. The powder had a BETspecific surface area of 15 m²/g, average secondary particle diameter of0.65 μm and adsorption of the surface treating agent of 2.9% by weight.

COMPARATIVE EXAMPLE 2

The procedures up to the hydrothermal treatment of Example 1 wererepeated, and the resulting reaction mixture was cooled, filtered andwashed with water. Then the de-watered product was thrown into astainless steel vessel containing i′on-exchange water, and into which0.667 liter of 1.0 mol/liter (as SiO₂) sodium metasilicate solution wasadded under stirring, followed by heating to 90° C. and 2 hours'stirring. Separately, 18.2 g of sodium stearate (purity: 86%) wasweighed and dissolved in 90° C. ion-exchange water, and the solution wasadded to the slurry under continued stirring to effect a surfacetreatment. Finally the system was filtered, washed with water, dried at95° C. for a day and night, and pulverized to provide a sample product.

Upon analysis, the composition of this product was identified to be:

Mg_(0.692)Al_(0.308)(OH)₂(HSi_(1.00)O_(3.00))_(0.154)(SO₄)_(0.054)(CO₃)_(0.023).062H₂O.The ratio of B anions in the total electric charge (x) was 0.50, themolar ratio of Si to Al₂O₃ was 1.00, the BET specific surface area was22 m²/g, average secondary particle diameter was 0.70 μm and theadsorption of the surface treating agent was 4.0% by weight.

COMPARATIVE EXAMPLE 3

A hydrotalcite compound was synthesized following “Embodiment 2” of Hei8 (1996)-217912A-JP (corres. to EP 708,056).

A liquid mixture of 3 liters of 1.5 mols/liter MgCl₂ solution and 0.667liter of 2.0 mol/liter AM(NO₃)₃ solution was put in an autoclave, andinto which 2.889 liters of 3.0 mols/liter NaOH solution was poured understirring, followed by about 30 minutes' stirring and then by ahydrothermal treatment at 170° C. for 12 hours. The system was thencooled to about 70° C., and into which 2.667 liters of 1.0 mol/liter (asSiO₂) sodium silicate (No. 3 water glass) solution was added understirring. The content of autoclave was further stirred for 3 minutes.Separately, 20.4 g of stearyl phosphate (purity: 99%) was weighed andsuspended in 70° C. diluted sodium hydroxide solution, which was pouredinto the autoclave under continued stirring to effect a surfacetreatment. Finally the system was filtered and the recovered solid waswashed with dicarbonated water, dried at 95° C. for a day and night, andpulverized to provide the product sample.

Upon analysis, the composition of this product was identified to be:

Mg_(0.692)Al0.308(OH)₂ (polymerized Si409O_(9.00))_(0.154).0.62H₂H₂O.The ratio of B anions in the total electric charge (x) was 0.00, themolar ratio of Si to Al₂O₃ was 4.00, the BET specific surface area was21 m²/g, average secondary particle diameter was 0.84 μm, and theadsorption of the surface treating agent was 4.0% by weight.

COMPARATIVE EXAMPLE 4

The product of Comparative Example 3 was further heat-treated at 200° C.for 3 hours to be removed of its interlayer water.

Upon analysis, the composition of the product was identified to be:

Mg_(0.692)Al_(0.308)(OH)₂ (polymerized Si4.00O_(9.00))_(0.154). 0.04H₂O.The ratio of B anions in the total electric charge (x) was 0.00, themolar ratio of Si to Al₂O₃ was 4.00, the BET specific surface area ofthe powder was 23m²/g, average secondary particle diameter was 0.80 μmand the adsorption of the surface treating agent was 4.4% by weight.

COMPARATIVE EXAMPLE 5

Two liters of 2.0 mols/liter AM(OH)₃ slurry was put in a stainless steelvessel, and into which 88.6 g of L₂CO₃ powder was added under stirring,followed by further 30 minutes' stirring. The reaction slurry wastransferred to an autoclave and given a hydrothermal treatment at 140°C. for 4 hours. After cooling off, the reaction slurry was transferredto a stainless steel vessel and heated to 80° C. Separately, 16.3 g ofsodium stearate (purity: 86%) was weighed and dissolved in 80° C.ion-exchange water. The solution was poured into the slurry to effect asurface treatment. Finally the system was filtered and washed withwater, dried at 95° C. for a day and night and pulverized to provide theproduct sample.

Upon analysis, the composition of the product was identified to be:Li_(1.00)Al₂(OH)₆(CO₃)_(0.50). 3.0H₂O. The BET specific surface area was15 m²/g, average secondary particle diameter was 0.90 μm and adsorptionof the surface treating agent was 2.9% by weight.

COMPARATIVE EXAMPLE 6

A hydrotalcite compound was synthesized following Example 4 of Hei 9(1997)-800828A (second)-JP (corres. to U.S. Pat. No. 5,767,179 and EP778,241).

Two liters of 2.0 mols/liter AM(OH)₃ slurry was put in a stainless steelvessel, and into which 88.6 g of Li₂CO₃ powder was added under stirring,followed by further 30 minutes' stirring. The reaction slurry wastransferred to an autoclave and given a hydrothermal treatment at 140°C. for 4 hours. After cooling the slurry to room temperature, 5.244liters of 0.5N HNO₃ solution was slowly poured into the autoclave understirring, followed by further 1 hour's stirring. Under continuedstirring, 2.010 liters of 1.0 mol/liter sodium silicate (No. 3 waterglass) solution was added, followed by another hour's stirring. Then thesystem was heated to 70° C. and into which 15.7 g of stearyl phosphate(purity: 99%) as suspended in 70° C. diluted sodium hydroxide solutionwas poured to effect a surface treatment. Finally the system wasfiltered, washed with decarbonated water, dried at 95° C. for a day andnight, and pulverized. Thus obtained product sample was heat-treated at200° C. for 3 hours to be removed of the interlayer water.

Upon analysis, the composition of the product was identified to be:Li_(1.00)Al₂(OH)₆ (polymerized Si_(2.00)O_(5.00))_(0.500).0.30H₂O. Theratio of B anions in the total electric charge (x) was. 0.00, the molarratio of Si to Al₂O₃ was 1.00, the BET specific surface area was 15m²/g, average secondary particle diameter was 0.90 μm and adsorption ofthe surface treating agent was 3.3% by weight.

COMPARATIVE EXAMPLE 7

A hydrotalcite compound was synthesized following Example 1 of Hei 9(1997)-800828A (second)-JP (corres. to U.S. Pat. No. 5,767,179 and EP778,241).

Two liters of 2.0 mols/liter AM(OH)₃ slurry was put in a stainless steelvessel, and into which 88.6 g of Li₂CO₃ powder and 0.040 liter of 1.0mol/liter MgCl₂ solution were added under stirring, followed by further30 minutes' stirring. The resulting reaction slurry was transferred intoan autoclave and given a hydrothermal treatment at 140° C. for 4 hours.Cooling the system to room temperature, 5.404 liters of 0.5N HNO₃solution was slowly poured into the autoclave under stirring, followedby further 1 hour's stirring. Under continued stirring, 2.090 liters of1.0 mol/liter sodium silicate (No. 3 water glass) solution was added,followed by another hour's stirring. Then the system was heated to 70°C. and into which 16.3 g of stearyl phosphate (purity: 99%) as suspendedin 70° C. diluted sodium hydroxide solution was poured into theautoclave to effect a surface treatment. Finally the system wasfiltered, washed with decarbonated water, dried at 95° C. for a day andnight, and pulverized. Thus obtained product sample was heat-treated at200° C. for 3 hours to be removed of the interlayer water.

Upon analysis, the composition of the product was identified to be:Li_(0.98)Mg_(0.02)Al₂(OH)₆ (polymerized Si_(2.00)O_(5.00))_(0.51).0.25H₂O The ratio of B anions in the total electric charge (x) was 0.00,the molar ratio of Si to Al₂O₃ was 1.02, the BET specific surface areawas 16 m²/g, average secondary particle diameter was 0.88 μm andadsorption of the surface treating agent was 3.2% by weight.

(Effect in Agricultural Film)

EVA was kneaded with other components according to the followingblending recipe, with 100° C. open roll mixer to provide EVA-based resincomposition, which was then molded into 100 μm-thick film with 180° C.electric hot pressing machine. As to each of the molded filmdispersibility of the infrared absorbing agent which was used thereinwas evaluated by visual observation based on formation of whiteblisters, and total light transmission and haze value (degree ofhaziness) were measured with hazemeter. Also infrared absorbing abilityof each film was measured and heat insulation index was calculated.

(EVA-based resin composition) Ethylene-vinyl acetate copolymer 87.4 wt%s (vinyl acetate content: 15%, 3758: Nippon Unicar Co.) Hindered aminephotostabilizer 0.2 wt % (TINUVIN 770: Ciba Geigy) Ultraviolet absorber0.1 wt % (TINUVIN 320: Ciba Geigy) Antioxidant (IRGANOX 1076: 0.1 wt %Ciba Geigy) Antihazing agent monoglycerine monostearate 1.5 wt %diglycerine distearate 0.5 wt % Lubricant (stearic acid amide) 0.1 wt %Antifogging agent 0.1 wt % (DS-403: Daikin Kogyo) Infrared absorbingagent 10 wt % (product of one of Examples or Comparative Examples)

EXAMPLE 15

In the EVA-based resin composition, the hydrotalcite compound of Example1 was used as infrared absorbing agent.

EXAMPLE 16

In the EVA-based resin composition, the hydrotalcite compound of Example2 was used as infrared absorbing agent.

EXAMPLE 17

In the EVA-based resin composition, the hydrotalcite compound of Example3 was used as infrared absorbing agent.

EXAMPLE 18

In the EVA-based resin composition, the hydrotalcite compound of Example4 was used as infrared absorbing agent.

EXAMPLE 19

In the EVA-based resin composition, the hydrotalcite compound of Example5 was used as infrared absorbing agent.

EXAMPLE 20

In the EVA-based resin composition, the hydrotalcite compound of Example6 was used as infrared absorbing agent.

EXAMPLE 21

In the EVA-based resin composition, the hydrotalcite compound of Example7 was used as infrared absorbing agent.

EXAMPLE 22

In the EVA-based resin composition, the hydrotalcite compound of Example8 was used as infrared absorbing agent.

EXAMPLE 23

In the EVA-based resin composition, the hydrotalcite compound of Example9 was used as infrared absorbing agent.

EXAMPLE 24

In the EVA-based resin composition,the hydrotalcite compound of Example10 was used as infrared absorbing agent.

EXAMPLE 25

In the EVA-based resin composition, the hydrotalcite compound of Example11 was used as infrared absorbing agent.

EXAMPLE 26

In the EVA-based resin composition, the hydrotalcite compound of Example12 was used as infrared absorbing agent.

EXAMPLE 27

In the EVA-based resin composition, the hydrotalcite compound of Example13 was used as infrared absorbing agent.

EXAMPLE 28

In the EVA-based resin composition, the hydrotalcite compound of Example14 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 8

In the EVA-based resin composition, the hydrotalcite compound ofComparative Example 1 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 9

In the EVA-based resin composition, the hydrotalcite compound ofComparative Example 2 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 10

In the EVA-based resin composition, the hydrotalcite compound ofComparative Example 3 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 11

In the EVA-based resin composition, the hydrotalcite compound ofComparative Example 4 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 12

In the EVA-based resin composition, the hydrotalcite compound ofComparative Example 5 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 13

In the EVA-based resin composition, the hydrotalcite compound ofComparative Example 6 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 14

In the EVA-based resin composition, the hydrotalcite compound ofComparative Example 7 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 15

In the EVA-based resin composition, no infrared absorbing agent wasblended.

The result of evaluation and measurements of the films of Examples 15-28and Comparative Examples 8-15 were as shown in Table 1.

TABLE 1 Heat insula- Total light Haze Dispersibility tion indextransmission value (visual observation) Example 15 85 89 4 good Example16 86 90 4 good Example 17 86 90 5 good Example 18 84 90 4 good Example19 84 90 5 good Example 20 86 90 4 good Example 21 86 90 5 good Example22 86 90 5 good Example 23 85 90 4 good Example 24 85 90 5 good Example25 84 90 4 good Example 26 84 90 5 good Example 27 85 90 5 good Example28 85 90 5 good Comparative 80 88 10 good Example 8 Comparative 82 88 10good Example 9 Comparative 83 89 10 good Example 10 Comparative 83 90 14good Example 11 Comparative 80 89 15 good Example 12 Comparative 84 8914 good Example 13 Comparative 84 89 14 good Example 14 Comparative 5592 2 — Example 15

Metallocene PE was used for formulating Metallocene PE-based resincompositions according to the following blending recipe. Eachcomposition was formed with a single screw kneader at 180° C., and thenmolded to a 100 μm-thick film with a T die extruder at 160° C. The filmswere evaluated and measured in the identical manner as done with theEVA-based films.

[Metallocene PE-based resin composition] Metallocene PE (KF-270: 87.3 wt% Nippon Polychem Co.) Hindered amine photostabilizer 0.2 wt % (TINUVIN622: Ciba Geigy) Ultraviolet absorber 0.1 wt % (TINUVIN 320: Ciba Geigy)Antioxidant (IRGANOX 1010: Ciba Geigy) 0.1 wt % (IRGAFOS 168: CibaGeigy) 0.1 wt % Antihazing agent monoglycerine monostearate 1.5 wt %diglycerine distearate 0.5 wt % Lubricant 0.1 wt % stearic acid amideAntifogging agent 0.1 wt % (KF-345, Shin-etsu Chemical Co.) Infraredabsorbing agent 10 wt % (Product of one of Examples or ComparativeExample)

EXAMPLE 29

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Example 2 was blended as infrared absorbing agent.

EXAMPLE 30

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Example 3 was blended as infrared absorbing agent.

EXAMPLE 31

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Example 4 was blended as infrared absorbing agent.

EXAMPLE 32

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Example 5 was blended as infrared absorbing agent.

EXAMPLE 33

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Example 6 was blended as infrared absorbing agent.

EXAMPLE 34

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Example 9 was blended as infrared absorbing agent.

EXAMPLE 35

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Example 13 was blended as infrared absorbing agent.

COMPARATIVE EXAMPLE 16

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Comparative Example 1 was blended as infrared absorbing agent.

COMPARATIVE EXAMPLE 17

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Comparative Example 2 was blended as infrared absorbing agent.

COMPARATIVE EXAMPLE 18

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Comparative Example 4 was blended as infrared absorbing agent.

COMPARATIVE EXAMPLE 19

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Comparative Example 5 was blended as infrared absorbing agent.

COMPARATIVE EXAMPLE 20

In the Metallocene PE-based resin composition, the hydrotalcite compoundof Comparative Example 6 was blended as infrared absorbing agent.

COMPARATIVE EXAMPLE 21

No infrared absorbing agent was blended in the Metallocene PE-basedresin composition.

COMPARATIVE EXAMPLE 22

Metallocene PE resin alone was used (without any additive).

The result of the evaluation and measurements the films of Examples29-35 and Comparative Examples 16-22 were as shown in Table 2.

TABLE 2 Heat insula- Total light Haze Dispersibility tion indextransmission value (visual observation) Example 29 77 90 4 good Example30 77 90 5 good Example 31 76 90 4 good Example 32 75 90 4 good Example33 77 89 5 good Example 34 76 90 4 good Example 35 77 89 4 goodComparative 67 89 8 good Example 16 Comparative 73 89 8 good Example 17Comparative 77 89 10 good Example 18 Comparative 72 88 13 good Example19 Comparative 77 88 11 good Example 20 Comparative 28 91 3 — Example 21Comparative 28 92 1 — Example 22

The above films were given an accelerated deterioration test withSunshine Weathermeter (Shimazu Seisakusho, Japan). Visual observationafter 750 hours' test found the film formed of Metallocene PE only ofComparative Example 22 heavily deteriorated (hardened). Also minorsurface deterioration and bleeding occurred in the film of ComparativeExample 21 which contained no infrared absorbing agent. All other filmsin which an infrared absorbing agent was blended showed less extent ofsurface deterioration compared to the film of Comparative Example 21,and also showed scarcely any bleeding.

PVC (Shin-Etsu Chemical Co.: average molecular weight, 1000) was usedfor formulating PVC-based resin coinpositions according to the followingblending recipe. Each composition was formed by kneading the componentswith 180° C. open roll mixer and was molded into 100 μm-thick film with180° C. hot electric pressing machine. The films were evaluated andmeasured in the identical manner as done with the EVA-based films.

[PVC-based resin composition] Polyvinyl chloride 57.89 wt % (averagemolecular weight: 1000 (Shin-Etsu Chemical Co) Plasticizer DOP (dioctylphthalate) 30 wt % Tricresyl phosphate 3 wt % Bisphenol A type epoxyresin 1.5 wt % Hindered amine photostabilizer 0.1 wt % (Chimassorb 119:Ciba Geigy) Ultraviolet absorber 0.05 wt % (TINUVIN 329: Ciba Geigy)Antioxidant 0.05 wt % (IRGANOX 1076: Ciba Geigy) Antihazing agent 1.0 wt% sorbitan monopalmitate Antifogging agent 0.1 wt % (KF-345, Shin-etsuChemical Co.) Lubricant 0.3 wt % methylene bis-stearic acid amide Heatstabilizer Ba-Zn-containing stabilizer 1.0 wt % Dibenzoylmethane 0.01 wt% Infrared absorbing agent 5. wt % (One of the products of Examples orcomparative materials)

EXAMPLE 36

In the PVC-based resin composition, the hydrotalcite compound of Example3 was used as infrared absorbing agent.

EXAMPLE 37

In the PVC-based resin composition, the hydrotalcite compound of Example7 was used as infrared absorbing agent.

EXAMPLE 38

In the PVC-based resin composition, the hydrotalcite compound of Example10 was used as infrared absorbing agent.

EXAMPLE 39

In the PVC-based resin composition, the hydrotalcite compound of Example14 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 23

In the PVC-based resin composition, the hydrotalcite compound ofComparative Example 1 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 24

In the PVC-based resin composition, the hydrotalcite compound ofComparative Example 4 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 25

In the PVC-based resin composition, the hydrotalcite compound ofComparative Example 7 was used as infrared absorbing agent.

COMPARATIVE EXAMPLE 26

In the PVC-based resin composition, infrared absorbing agent was used.

Results of evaluating the performance of the films of Examples 36-39 andComparative Examples 23-26 are shown in Table 3.

TABLE 3 Heat insula- Total light Haze Dispersibility tion indextransmission value (visual observation) Example 36 89 91 5 good Example37 89 91 4 good Example 38 89 91 4 good Example 39 89 91 4 goodComparative 85 91 5 good Example 23 Comparative 88 90 6 good Example 24Comparative 88 91 6 good Example 25 Comparative 78 91 3 — Example 26

Also FIG. 1 shows an IR absorption chart of a 100 μm-thick film ofmetalocene polyethylene (PE) containing 10 wt % of the hydrotalcitecompound (powder) of Example 2 of the present invention.

FIG. 2 shows an IR absorption chart of a 100 μm-thick film ofmetallocene PE containing 10 wt % of the hydrotalcite compound (powder)of Example 3 of the present invention.

FIG. 3 shows an IR absorption chart of a 100 μm-thick film ofmetallocene PE containing 10 wt % of the hydrotalcite compound (powder)of Example 9 of the present invention.

FIG. 4 shows an IR absorption chart of a 100 μm-thick film ofmetallocene PE containing 10 wt % of the hydrotalcite compound (powder)of Comparative Example 1.

FIG. 5 shows an IR absorption chart of a 100 μm-thick film ofmetallocene PE alone.

INDUSTRIAL UTILIZABILITY

The hydrotalcite compound which contains as interlayer anions at leastone of silicon-, phosphorus- and boron-containing oxygen acid ions, apart or whole of said anions being at least silicon-, phosphorus- andboron-containing polymerized oxygen acid anions; and at least one otherkind of anions, exhibits excellent infrared absorbing ability ascompared to that of conventional hydrotalcite compounds; and at the sametime, when it is blended in thermoplastic resin to be used foragricultural film, it can impart excellent light transmission to thefilm. In particular, said hydrotalcite compound having an averagesecondary particle diameter of not more than 5 μm and BET specificsurface area of not more than 30 m²/g or the same which issurface-treated shows excellent dispersibility in the thermoplasticresin to be used for making the film. In the occasion of preparing ahydrotalcite compound of the present invention, less cost is incurredwhen a sulfate ion-type compound is prepared from the time of thesynthesizing reaction.

When the hydrotalcite compound of the present invention is contained inagricultural film as infrared absorbing agent, agricultural filmexcelling in both heat insulation property and light transmission can beprovided. Furthermore, by concurrent use of various additives,agricultural film excelling in weatherability, anti-hazing property,anti-fogging property, dust resistance, water repellence, toughness,agricultural chemical resistance, acid precipitation resistance, heatresistance, snti-fading property, antibacterial property, antimoldproperty, spreading processability and prevention of resin degradationcaused by the various additives, and furthermore excelling in durabilityof those favorable properties can be provided.

What is claimed is:
 1. A hydrotalcite compound, which has the followingformula (1) or (2) and which holds in its interlayer at least a kind ofanions selected from silicon-, phosphorus- and boron-containing oxygenacid ions, at least a part of said anions being at least one ofsilicon-, phosphorus- and boron-containing polymerized oxygen acid ions,and at least a kind of anions other than said oxygen acid anions, (Mg—Alhydrotalcite compound)

in which M²⁺ stands for at least a kind of divalent metal ion of Zn, Caand Ni, A stands for at least a kind of anion selected from silicon-,phosphorus- and boron-containing oxygen acid ions, at least a part ofwhich being at least a kind of anion selected from silicon-, phosphorus-and boron-containing polymerized oxygen acid ions, B stands for at leasta kind of anion other than the A, and x, y₁, y₂, z₁, z₂ and b eachsatisfies the following condition or conditions: x: 0<x≦0.5, y₁ and y₂:y₁+y₂=1, 0<y₁<1, 0≦y₂<1, z₁ and z₂: 0<z₁, 0<z₂, b: 0≦b<2; (Li—Alhydrotalcite compound)

 in which G²⁺ stands for at least a kind of divalent metal ion of Mg,Zn, Ca and Ni, A stands for at least a kind of anion selected fromsilicon-, phosphorus- and boron-containing oxygen acid ions, at least apart of which being at least a kind of anion selected from silicon-,phosphorus- and boron-containing polymerized oxygen acid ions, B standsfor at least a kind of anion other than the A, and y₁, y₂, x, z₁, z₂ andb each satisfies the following condition or conditions: y₁ and y₂:0<y₁≦1, 0≦y₂<1, 0.5≦(y₁+y₂)≦1, x: x=y₁+2y₂, z₁ and z₂: 0<z₁, 0<z₂, b:0≦b<5.
 2. A hydrotalcite compound as described in claim 1, in which ananion expressed by B in the formula (1) or (2) is at least a kind ofanion selected from sulphate ion, carbonate ion, chloride ion andnitrate ion.
 3. A hydrotalcite compound as described in claim 1, inwhich the anion expressed by B in the formula (1) or (2) is at least akind of anion selected from sulphate ion and carbonate ion.
 4. Ahydrotalcite compound as described in claim 1, in which the hydrotalcitecompound of the formula (1) or (2) satisfies the following formula:0.1≦(total electric charge number of (B)z₁)/x≦0.8.
 5. A hydrotalcitecompound as described in claim 1, in which the silicon- and/orphosphorus-containing oxygen acid ions which is the anion expressed as Ain the formula (1) is present within the range defined by the followingformula wherein Q stands for the mol number of Si and/or P:  0<Q/(molnumber as Al₂O₃)<2.
 6. A hydrotalcite compound as described in claim 1,in which the silicon-containing oxygen acid ions which is the anionexpressed as A in the formula (2) is present within the range defined bythe following formula wherein R stands for the mol number of Si:0<R/(mol number as Al₂O₃)<1.
 7. A hydrotalcite compound as described inclaim 1, which is surface-treated with at least a surface treating agentof the group comprising higher fatty acids, anionic surfactants,phosphoric acid esters, nonionic surfactants, silane-, titanate- andaluminum-containing coupling agents and fatty acid esters polyhydricalcohols.
 8. A hydrotalcite compound as described in claim 1, which hasan average secondary particle diameter of not more than 5 μm and a BETspecific surface area of not more than 30 m²/g.
 9. An infrared absorbingagent containing as the active ingredient a hydrotalcite compound asdescribed claim
 1. 10. An infrared absorbing agent containing as theactive ingredient a hydrotalcite compound as described in claim 1, fromwhich a part or whole of the interlayer water has been removed.
 11. Aprocess for preparing a hydrotalcite compound as described in claim 1,which comprises preparing in advance a hydrotalcite compound whoseinterlayer anions are mainly sulfate ions at the time of thesynthesizing reaction, and thereafter exchanging the ions with at leasta kind of anion of silicon-, phosphorus- and boron-containing oxygenacid ions, a part or whole of said ions being at least one of silicon-,phosphorus- and boron-containing polymerized oxygen acid ions, attemperatures ranging from 60-100° C.
 12. A hydrotalcite compound asdescribed in claim 2, in which the anion expressed by B in the formula(1) or (2) is at least a kind of anion selected from sulphate ion andcarbonate ion.
 13. A hydrotalcite compound as described in claim 2 inwhich the hydrotalcite compound of the formula (1) or (2) satisfies thefollowing formula: 0.1≦(total electric charge number of (B)z₁/x≦0.8. 14.A hydrotalcite compound as described in claim 2, in which the silicon-and/or phosphorus-containing oxygen acid ions which is the anionexpressed as A in the formula (1) is present within the range defined bythe following formula wherein Q stands for the mol number of Si and/orP: 0<Q/(mol number as Al₂O₃)<2.
 15. A hydrotalcite compound as describedin claim 2, in which the silicon-containing oxygen acid ions which isthe anion expressed as A in the formula (2) is present within the rangedefined by the following formula wherein R stands for the mol number ofSi: 0<R/(mol number as Al₂O₃)<1.
 16. A hydrotalcite compound asdescribed in claim 2, which is surface-treated with at least a surfacetreating agent of the group comprising higher fatty acids, anionicsurfactants, phosphoric acid ester, nonionic surfactants, silane-,titanate- and aluminum-containing coupling agents and fatty acid estersof polyhydric alcohols.
 17. A hydrotalcite compound as described inclaim 2, which has an average secondary particle diameter of not morethan 5 μm and a BET specific surface area of not more than 30 m²/g. 18.An infrared absorbing agent containing as the active ingredient ahydrotalcite compound as described in claim
 2. 19. An infrared absorbingagent containing as the active ingredient a hydrotalcite compound asdescribed in claim 2, from which a part or whole of the interlayer waterhas been removed.
 20. A process for preparing a hydrotalcite compound asdescribed in claim 2, which comprises preparing in advance ahydrotalcite compound whose interlayer anions are mainly sulfate ions atthe time of the synthesizing reaction, and thereafter exchanging theions with at least a kind of anion of silicon-, phosphorus- andboron-containing oxygen acid ions, a part or whole of said ions being atleast one of silicon-, phosphorus- and boron-containing polymerizedoxygen acid ions, at temperatures ranging from 60-100° C.
 21. Ahydrotalcite compound as described in claim 3, in which the hydrotalcitecompound of the formula (1) or (2) satisfies the following formula:0.1≦(total electric charge number of (B)z₁/x≦0.8.
 22. A hydrotalcitecompound as described in claim 3, in which the silicon- and/orphosphorus-containing oxygen acid ions which is the anion expressed as Ain the formula (1) is present within the range defined by the followingformula wherein Q stands for the mol number of Si and/or P: 0<Q/(molnumber as Al₂O₃)<2.
 23. A hydrotalcite compound as described in claim 3,in which the silicon-containing oxygen acid ions which is the anionexpressed as A in the formula (2) is present within the range defined bythe following formula wherein R stands for the mol number of Si:0<R/(mol number as Al₂O₃)<1.
 24. A hydrotalcite compound as described inclaim 3, which is surface-treated with at least a surface treating agentof the group comprising higher fatty acids, anionic surfactants,phosphoric acid esters, nonionic surfactants, silane-, titanate- andaluminum-containing coupling agents and fatty acid esters of polyhydricalcohols.
 25. A hydrotalcite compound as described in claim 3, which hasan average secondary particle diameter of not more than 5 μm and a BETspecific surface area of not more than 30 m²/g.
 26. An infraredabsorbing agent containing as the active ingredient a hydrotalcitecompound as described in claim
 3. 27. An infrared absorbing agentcontaining as the active ingredient a hydrotalcite compound as describedin claim 3, from which a part or whole of the interlayer water has beenremoved.
 28. A process for preparing a hydrotalcite compound asdescribed in claim 3, which comprises preparing in advance ahydrotalcite compound whose interlayer anions are mainly sulfate ions atthe time of the synthesizing reaction, and thereafter exchanging theions with at least a kind of anion of silicon-, phosphorus- andboron-containing oxygen acid ions, a part or whole of said ions being atleast one of silicon-, phosphorus- and boron-containing polymerizedoxygen acid ions, at temperatures ranging from 60-100° C.
 29. Ahydrotalcite compound as described in claim 4, in which the silicon-and/or phosphorus-containing oxygen acid ions which is the anionexpressed as A in the formula (1) is present within the range defined bythe following formula wherein Q stands for the mol number of Si and/orP: 0<Q/(mol number as Al₂O₃)<2.
 30. A hydrotalcite compound as describedin claim 4, in which the silicon-containing oxygen acid ions which isthe anion expressed as A in the formula (2) is present within the rangedefined by the following formula wherein R stands for the mol number ofSi: 0<R/(mol number as Al₂O₃)<1.
 31. A hydrotalcite compound asdescribed in claim 4, which is surface-treated with at least a surfacetreating agent of the group comprising higher fatty acids, anionicsurfactants, phosphoric acid esters, nonionic surfactants, silane-,titanate- and aluminum-containing coupling agents and fatty acid estersof polyhydric alcohols.
 32. A hydrotalcite compound as described inclaim 4, which has an average secondary particle diameter of not morethan 5 μm and a BET specific surface area of not more than 30 m²/g. 33.An infrared absorbing agent containing as the active ingredient ahydrotalcite compound as described in claim
 4. 34. An infrared absorbingagent containing as the active ingredient a hydrotalcite compound asdescribed in claim 4, from which a part or whole of the interlayer waterhas been removed.
 35. A process for preparing a hydrotalcite compound asdescribed in claim 4, which comprises preparing in advance ahydrotalcite compound whose interlayer anions are mainly sulfate ions atthe time of the synthesizing reaction, and thereafter exchanging theions with at least a kind of anion of silicon-, phosphorus- andboron-containing oxygen acid ions, a part or whole of said ions being atleast one of silicon-, phosphorus- and boron-containing polymerizedoxygen acid ions, at temperatures ranging from 60-100° C.
 36. Ahydrotalcite compound as described in claim 5, which is surface-treatedwith at least a surface treating agent of the group comprising higherfatty acids, anionic surfactants, phosphoric acid esters, nonionicsurfactants, silane-, titanate- and aluminum-containing coupling agentsand fatty acid esters of polyhydric alcohols.
 37. A hydrotalcitecompound as described in claim 5, which has an average secondaryparticle diameter of not more than 5 μm and a BET specific surface areaof not more than 30 m²/g.
 38. An infrared absorbing agent containing asthe active ingredient a hydrotalcite compound as described in claim 5.39. An infrared absorbing agent containing as the active ingredient ahydrotalcite compound as described in claim 5, from which a part orwhole of the interlayer water has been removed.
 40. A process forpreparing a hydrotalcite compound as described in claim 5, whichcomprises preparing in advance a hydrotalcite compound whose interlayeranions are mainly sulfate ions at the time of the synthesizing reaction,and thereafter exchanging the ions with at least a kind of anion ofsilicon-, phosphorus- and boron-containing oxygen acid ions, a part orwhole of said ions being at least one of silicon-, phosphorus- andboron-containing polymerized oxygen acid ions, at temperatures rangingfrom 60-100° C.
 41. A hydrotalcite compound as described in claim 6,which is surface-treated with at least a surface treating agent of thegroup comprising higher fatty acids, anionic surfactants, phosphoricacid esters, nonionic surfactants, silane-, titanate- andaluminum-containing coupling agents and fatty acid esters of polyhydricalcohols.
 42. A hydrotalcite compound as described in claim 6, which hasan average secondary particle diameter of not more than 5 μm and a BETspecific surface area of not more than 30 m²/g.
 43. An infraredabsorbing agent containing as the active ingredient a hydrotalcitecompound as described in claim
 6. 44. An infrared absorbing agentcontaining as the active ingredient a hydrotalcite compound as describedin claim 6 from which a part or whole of the interlayer water has beenremoved.
 45. A process for preparing a hydrotalcite compound asdescribed in claim 6, which comprises preparing in advance ahydrotalcite compound whose interlayer anions are mainly sulfate ions atthe time of the synthesizing reaction, and thereafter exchanging theions with at least a kind of anion of silicon-, phosphorus- andboron-containing oxygen acid ions, a part or whole of said ions being atleast one of silicon-, phosphorus- and boron-containing polymerizedoxygen acid ions, at temperatures ranging from 60-100° C.
 46. Ahydrotalcite compound as described in claim 7, which has an averagesecondary particle diameter of not more than 5 μm and a BET specificsurface area of not more than 30 m²/g.
 47. An infrared absorbing agentcontaining as the active ingredient a hydrotalcite compound as describedin claim
 7. 48. An infrared absorbing agent containing as the activeingredient a hydrotalcite compound as described in claim 7, from which apart or whole of the interlayer water has been removed.
 49. A processfor preparing a hydrotalcite compound as described in claim 7, whichcomprises preparing in advance a hydrotalcite compound whose interlayeranions are mainly sulfate ions at the time of the synthesizing reaction,and thereafter exchanging the ions with at least a kind of anion ofsilicon-, phosphorus- and boron-containing oxygen acid ions, a part orwhole of said ions being at least one of silicon-, phosphorus- andboron-containing polymerized oxygen acid ions, at temperatures rangingfrom 60-100° C.
 50. An infrared absorbing agent containing as the activeingredient a hydrotalcite compound as described in claim
 8. 51. Aninfrared absorbing agent containing as the active ingredient ahydrotalcite compound as described in claim 8, from which a part orwhole of the interlayer water has been removed.
 52. An agricultural filmhaving a film structure containing 1-30% by weight of the thermoplasticresin constituting said film of at least an infrared absorbing agentwhich is described in claim
 9. 53. An agricultural film having a filmstructure containing 1-30% by weight of the thermoplastic resinconstituting said film of at least an infrared absorbing agent which isdescribed in claim 10.